Southern  Branch 
of  the 

University  of  California 

Los  Angeles 

Form  L-l 


This  book  is  DUE  on  last  date  stamped  below 


*  4 


t9 


1958 


BOOKS 

BY 

MINNIE  GOODNOW,  R.  N. 

First-Year  Nursing 
12mo    of    351    pages,    illustrated. 
Cloth,  $1.75  net.         Second  Edition. 

Outlines  of  Nursing  History 
12mo  of  370  pages,  with  88  illus- 
trations. Cloth,  $2.00  net. 

War  Nursing 

12mo    of    172    pages,    illustrated. 
Cloth,  $1.50  net. 

Practical  Physics  for  Nurses 
12mo  of  203  pages,  with  100  illus- 
trations. Just  Ready. 


PRACTICAL  PHYSICS 
FOR  NURSES 


By 

MINNIE  GOODNOW,  R.  N. 

Author  of  "  First-Year  Nursing,"  "  Outlines  of  Nursing  History," 
"  War  Nursing,"  "Ten  Lessons  in  Chemistry  for  Nurses,"  and  "The 
Nursing  of  Children";  formerly  Directress  of  Nurses,  Milwaukee 
County  Hospital;  formerly  Superintendent  of  the  Woman's  Hospital, 
Denver,  and  of  the  Bronsonl  Hospital,  Kalamazoo ;  Specialist  in 
Hospital  Equipment 


WITH  100  ILLUSTRATIONS 


PHILADELPHIA  AND  LONDON 

W.    B.    SAUNDERS    COMPANY 

1919 


Copyright,  1919,  by  W.  B.  Saunders  Company 


PAINTED    IN    AMERICA 

PRESS    OF 

W.    B.    SAUNDERS    COMPANY 
PHILADELPHIA 


G 


FOREWORD 


THE   criticism  is  often  made  that   nurses   are   not 

intelligent  about  the  handling  of  ordinary  household 

.   and  hospital  appliances,  and  that  they  make  no  attempt 

A1   to  understand  the  workings  of  plumbing,  heating  and 

£  ventilating  apparatus,  surgical  instruments  and  appa- 

_,  ratus,  etc. 

The  fault  lies  not  so  much  in  the  nurse  herself,  nor 

•  in  any  lack  of  inclination  to  learn,  as  it  does  in  the  fact 
N    that  she  has  not  been  taught  the  laws  which  govern 
&  some  of  the  simplest  activities  of   life.      Very  many 
**  nurses  are  not  high-school  graduates,  and  of  those  who 

are,  not  all  have  studied  physics,  nor  know  how  to 

•  apply  their  knowledge  to  nursing. 

I  Both  Physics  and  Chemistry  are  of  great  impor- 
I  tance  to  a  nurse,  because  they  are,  at  bottom,  sciences 
of  common  life.  The  human  anatomy  is  built  in  accord- 
ance with  the  laws  of  physics,  and  its  movements  are 
governed  by  them.  It  is  necessary,  therefore,  if  a 
nurse  is  to  do  intelligent  work,  that  she  should  know 
some  of  the  existing  laws  of  physics,  and  how  her 
patients,  her  hospital  environment,  and  all  her  work  are 
controlled  by  them. 

This  subject  has  been  a  much-neglected  one  in 
hospital  training-schools,  chiefly  because  there  was  no 
text-book  concerning  it  which  was  suited  to  nurses. 

13 


14  FOREWORD 

The  following  lessons  have  been  prepared  in  the  endeavor 
to  give  briefly  some  of  the  more  important  laws  of 
physics,  especially  those  which  apply  to  daily  life  and 
to  a  nurse's  work.  No  effort  has  been  made  to  cover 
the  whole  subject,  but  only  to  select  from  it  some  of  the 
principles  which  apply  most  obviously  and  directly  to 
hospital  life  and  to  nursing.  There  are  many  laws  of 
physics  not  even  mentioned  in  the  following  pages. 

The  apparatus  and  supplies  for  the  illustrative  ex- 
periments are  of  the  simplest  sort.  Most  hospitals  will 
already  have  them  in  stock. 

The  author  wishes  to  acknowledge  her  indebtedness 
to  Mr.  William  H.  Smiley,  educator,  and  to  Dr.  Horace 
Greeley  Wetherill,  surgeon,  for  careful  and  invaluable 
criticism  of  the  manuscript,  and  to  Miss  Kinsey  for  cor- 
rection. 

MINNIE  GOODNOW,  R.  N.. 

September,  1919. 


CONTENTS 


PAGE 

SUPPLIES 17 

INTRODUCTION..  . 


CHAPTER  I 
MATTER.     ITS  COMPOSITION.  . . 


CHAPTER  II 
MECHANICS 32 

CHAPTER  III 
MECHANICS  (Continued) 41 

CHAPTER  IV 
HYDRAULICS 60 

CHAPTER  V 
PNEUMATICS 73 

CHAPTER  VI 
PNEUMATICS  (Continued) 85 

CHAPTER  VII 
HEAT 98 

CHAPTER  VIII 
HEAT  (Continued) 115 

CHAPTER  IX 
SOUND 130 

CHAPTER  X 
LIGHT. . .  .   141 


16  CONTENTS 

CHAPTER  XI  PAGE 

ELECTRICITY 163 

CHAPTER  XII 
THE  X-RAY.     RADIUM 180 

CHAPTER  XIII 
QUESTIONS  FOR  REVIEW  OF  PRINCIPLES  AND  ORIGINAL  THINKING  190 


INDEX .   197 


PRACTICAL  PHYSICS  FOR  iNURSES 


SUPPLIES 

THE  following  will  be  sufficient  to  enable  one  to  make 
the  experiments  suggested  in  this  book: 

Two  quart  flasks. 

Several  large  corks,  one  which  shall  fit  flask,  being  perforated 

for  two  tubes. 
Glass  tubing,  pieces  6  to  18  inches  long,  two  sizes;  one  piece 

bent  into  a  U-shape. 

Rubber  tubing,  a  few  short  pieces  to  fit  glass  tubing. 
One  dozen  test-tubes,  with  holder. 
A  few  microscope  slides. 

Two  bath  thermometers,  or  other  unmounted  thermometers. 
One  thermometer  with  scale  to  250°  F. 
A  glass  prism. 
A  square  bottle. 
Two  lamp  chimneys. 
Small   quantities  of   sulphuric    acid,   copper   sulphate,   alum, 

sugar,  touch-paper. 

APPARATUS 

If  possible,  bring  into  class  or  arrange  to  have  class  see 
the  following: 

Axis-traction  forceps. 

Bulb  syringe. 

Electric  cautery. 

Electric  battery  or  cell,  wet  form. 

Electric  toaster. 

Glass  dressing  syringe. 

Glass  irrigator,  with  uterine  point. 

2  I7 


18  PRACTICAL  PHYSICS  FOR  NURSES 

Head-mirror. 

Hypodermic  syringe. 

Laryngoscope. 

Microscope. 

Obstetric  chart,  showing  progress  through  pelvis. 

Rectal  dilators. 

Reading  glass. 

Stomach-tube. 

Sphygmomanometer. 

Urine  centrifuge. 

Urinometer. 

Uterine  dilator. 

x-Ray  apparatus. 


INTRODUCTION 

Physics  is  the  science  of  every-day  life,  and  relates 
to  most  of  our  ordinary  activities.  The  wind  and 
weather,  our  houses  and  their  contents,  all  work  and 
play,  all  personal  and  commercial  activities  involve  the 
laws  of  physics. 

We  find  ourselves  annoyed  or  defeated  because  things 
"won't  work"  as  we  wish  them  to.  Usually  the  reason 
is  that  we  are  attempting  to  make  them  act  in  opposi- 
tion to  the  laws  of  nature;  we  do  this  because  we  do  not 
know  what  those  laws  are,  nor  to  what  extent  they 
govern  the  world.  A  very  elementary  knowledge  of 
these  common  laws  will  not  only  help  us  to  do  our  daily 
tasks  with  greater  ease,  but  will  make  them  vastly 
more  interesting  and  meaningful. 

A  knowledge  of  physics  is  essential  not  only  to  the 
skilful  use  of  hospital  and  nursing  appliances  and  equip- 
ment, but  to  an  understanding  of  the  structure  and  func- 
tions of  the  human  body.  Dr.  John  C.  Draper  says: 
"There  is  not  a  tissue,  organ,  nor  function  of  the  body 
the  proper  comprehension  of  which  does  not  involve  a 
knowledge  of  the  laws  of  physics.  There  is  hardly  a 
principle  of  physics  which  does  not  apply  to  the  human 
body." 

The  bony  structure,  the  attachment  of  muscles,  the 

19 


20  PRACTICAL  PHYSICS  FOR  NURSES 

working  of  the  heart,  blood-vessels  and  respiratory 
organs,  the  acts  of  seeing  and  hearing,  etc.,  all  depend 
upon  the  laws  of  physics;  while  apparatus  and  ap- 
pliances for  the  treatment  of  disease  can  hardly  be  used 
intelligently  or  effectively  without  a  comprehension  of 
these  same  laws. 

Physics,  in  its  logical  limits,  is  an  abstruse  and  diffi- 
cult subject.  The  fundamental  principles  are,  however, 
extremely  simple  and  can  be  understood  even  by  un- 
trained minds.  The  mere  committing  to  memory  of 
some  of  its  laws  will  serve  to  elucidate,  throughout 
one's  life,  many  appliances  and  occurrences. 

It  is  recommended  that  all  the  experiments  given, 
however  simple  or  familiar,  be  actually  made  in  class, 
so  that  the  full  force  of  their  meaning  and  application 
may  come  at  the  psychologic  moment. 


CHAPTER  I 
MATTER.    ITS  COMPOSITION 

MAN  has  always  been  eager  to  know  of  what  things 
were  made,  and  why  inanimate  objects  act  as  they  do. 
Physics  and  Chemistry  are  the  two  sciences  which 
have  been  developed  in  this  search  for  knoweldge. 
Chemistry  is,  in  reality,  a  branch  of  Physics. 

Physics  is  the  science  of  matter,  its  properties,  changes, 
and  motions. 

Matter  is  anything  which  we  can  see,  feel,  or  handle; 
anything  which  occupies  space. 

Simple  and  Complex  Substances.- — Some  substances, 
or  portions  of  matter,  are  simple;  some  are  complex. 

Wood,  for  example,  is  a  complex  substance.  If,  in 
attempting  to  find  out  of  what  it  is  made,  we  divide 
it  into  minute  pieces,  we  spoil  or  destroy  it  and  cannot 
make  it  into  wood  again.  If  we  heat  it,  we  also  de- 
stroy it. 

Iron,  on  the  other  hand,  is  a  simple  substance.  If 
we  divide  it  into  ever  so  fine  particles,  we  can  still  iden- 
tify it  as  iron;  if  we  heat  it  ever  so  hot,  as  soon  as  it 
cools  it  is  plainly  iron ;  we  have  not  spoiled  nor  destroyed 
it  by  what  we  have  done  to  it. 

The  Ultimate  Composition  of  Matter.— With  even  the 


22  PRACTICAL  PHYSICS  FOR  NURSES 

simplest  substance,  after  we  have  divided  it  into  the 
smallest  particles  possible,  we  have  not  found  out  its 
real  composition.  We  imagine  that  if  we  were  able  to 
divide  it  still  further  we  might  get  at  this  knowledge. 
We  find  that  scientists  have  been  able,  in  what  seem 
rather  roundabout  ways,  but  which  are  none  the  less 
exact,  to  accomplish  this. 

Scientists  have  agreed  that  all  matter  is  made  up  of 
tiny  particles,  called  molecules,1  which  in  a  simple  sub- 
stance like  iron  are  all  alike. 

It  is  agreed  that  molecules  are  composed  of  still  smaller 
particles,  called  atoms,  which  may  or  may  not  be  alike, 
but  which  together  form  a  definite  substance,  either 
simple  or  complex.  There  may  be  few  or  many  atoms 
in  a  molecule,  the  number  varying  from  two  to  fifty  or 
more. 

The  assumption  that  matter  is  composed  of  mole- 
cules, which  are  themselves  composed  of  atoms,  is  called 
the  Atomic  Theory,  While  merely  a  theory  which  it 
is  not  possible  to  prove,  it  so  well  accounts  for  every- 
thing which  man  has  observed  that  it  is  generally  ac- 
cepted as  fact. 

A  particle  is  the  smallest  subdivision  of  matter  that 
can  be  obtained  by  mechanical  means. 

A  molecule  is  the  smallest  portion  of  matter  which 
can  exist  alone. 

1  It  is  estimated  that  there  are  2,000,000,000,000,000,000,000,000 
molecules  in  a  drop. 


MATTER.    ITS  COMPOSITION  23 

An  atom  is  the  smallest  portion  of  matter  which  can 
exist  in  combination. 

Much  modern  research  has  been  directed  toward 
discovering  the  make-up  of  atoms;  the  electron  theory 
has  been  formulated,  and  is  by  some  scientists  regarded 
as  proved.  This  theory  holds  that  each  atom  is  com- 
posed of  many  infinitely  small  particles,  which  are 
called  corpuscles.  All  of  these  corpuscles  are  electric- 
ally charged,  part  of  them  being  positive  and  part 
negative;  such  being  the  case,  they  mutually  attract 
one  another  and  hold  together  to  form  the  atom.  Heat 
or  other  forces  may  loosen  the  attraction,  so  that  some 
of  the  negatively  electrified  corpuscles  may  fall  off,  in 
which  case  they  promptly  attach  themselves  to  some 
other  atom.  In  certain  substances  which  we  call 
"radio-active"  (See  Chapter  XII)  corpuscles  are  more 
or  less  constantly  and  forcibly  being  expelled  from  the 
atom. 

Physics  concerns  itself  with  molecules.  Chemistry 
concerns  itself  with  atoms,  and  deals  with  the  minute 
structures  and.  change  of  matter. 

Chemical  and  Physical  Changes. — If  we  heat  water 
to  the  boiling-point,  it  changes  into  steam.  If  we  sub- 
ject it  to  sufficient  cold,  it  changes  into  ice.  These  are 
changes  inform  only.  They  are  called  physical  changes. 

If  we  heat  sugar,  it  melts,  bubbles,  boils,  turns  brown, 
gives  off  smoke,  and  finally  becomes  a  charred,  black 
mass,  which  is  plainly  no  longer  sugar. 


24  PRACTICAL  PHYSICS  FOR  NURSES 

Experiment. — Take  a  small  tin  plate  or  dish,  grasp  it  with  for- 
ceps, place  on  it  a  small  amount  of  white  sugar,  and  hold  it  over  a 
gas,  alcohol,  or  other  flame.  Note  the  various  changes  which  take 
place  as  the  heating  progresses,  and  the  resulting  black  mass,  which 
is  almost  pure  carbon.  This  is  a  change  in  composition.  It  is 
called  a  chemical  change. 

A  physical  change  is  a  change  in  inform  of  a  substance. 
A  chemical  change  is  a  change  in  the  composition  of  a 
substance. 

PROPERTIES  OF  MATTER 

The  molecules  of  any  substance,  no  matter  how  com- 
pact it  seems  to  be,  do  not  touch  each  other.  In  hard, 
firm  substances  they  are  close  together;  in  soft  or  loose 
substances,  further  apart;  but  they  are  always  slightly 
separated,  the  distance  between  being  very  little,  yet 
enough  to  admit  of  motion.  (See  Heat.} 

The  force  which  holds  molecules  in  place  or  together 
is  called  cohesion. 

The  force  which  holds  atoms  together  is  called  chemical 
affinity. 

Cohesion  holds  molecules  of  the  same  sort  together, 
as  iron  to  iron.  It  is  cohesion  which  makes  an  iron  bar 
or  a  piece  of  wood  firm  and  strong. 

Adhesion  is  the  force  which  holds  molecules  of  unlike 
substances  together;  for  example,  grease  or  dirt  adheres 
to  a  utensil. 

Experiment. — Press  two  plates  of  glass  (microscope  slides  or 
window  glass)  together.  You  will  find  it  somewhat  difficult  to 
separate  them;  it  is  most  easily  done  by  sliding,  which  separates 
them  particle  by  particle.  Wet  the  surface  with  water  or  oil  and 
again  press  together;  they  will  separate  with  still  greater  difficulty. 
The  water  or  oil  has  greater  adhesion  than  the  glass. 


MATTER.    ITS  COMPOSITION  25 

Reduce  the  force  of  cohesion  and  you  increase  the 
force  of  adhesion.  Water  or  oil  has  less  cohesion  than 
glass — i.  e.,  is  less  firmly  held  together — and  therefore 
adheres  more  closely  to  the  solid  object.  Grind  rock 
salt  to  powder  and  it  dissolves  more  readily;  the  cohesion 
in  the  large  lump  being  broken  up,  adhesion  between 
the  salt  and  water,  unlike  substances,  takes  place  more 
easily. 

Some  of  the  properties,  or  inherent  qualities,  of  matter 
are  as  follows: 

GENERAL  PROPERTIES 

Extension  is  self-evident.  Divisibility  is  also  self- 
evident. 

Mobility. — It  is  readily  apparent  that  all  substances 
are  movable  if  sufficient  force  is  applied. 

Impenetrability. — One  thing  cannot  occupy  the  same 
space  as  another  at  the  same  time.  In  instances  where 
it  seems  to  occur,  as  when  a  sponge  is  placed  in  water, 
it  is  merely  that  the  molecules  of  one  substance  are 
between  those  of  the  other;  the  water,  in  this  case,  fits 
around  the  sponge,  but  is  not  occupying  the  same 
space. 

Experiment. — Fit  a  funnel  tightly  into  the  mouth  of  a  bottle, 
so  that  no  air  can  pass  around  the  stem  of  the  funnel.  Pour  water 
into  the  funnel;  only  a  little  of  it  runs  into  the  bottle,  though  the 
latter  is  apparently  empty.  Why?  Because  the  bottle  is  already 
full  of  air.  Loosen  the  funnel  so  that  the  air  in  the  bottle  can  es- 
cape, and  the  water  readily  runs  in.  Difficulty  in  filling  a  hot- 
water  bag  arises  when  so  large  a  stream  of  water  is  used  that  it 
blocks  the  exit  of  the  air;  a  smaller  stream  overcomes  the  difficulty. 


26  PRACTICAL  PHYSICS  FOR  NURSES 

Inertia  is  a  quality  which  all  matter  possesses  to  a 
marked  degree.  It  is  the  property  which  makes  matter, 
when  let  alone,  continue  to  do  what  it  is  doing.  If  it  is 
moving,  it  tends  to  keep  on.  If  it  is  at  rest,  it  tends  to 
remain  so.  When  we  attempt  to  move  an  object,  we 
feel  the  resistance  of  its  inertia;  when  we  attempt  to 
stop  a  moving  object,  we  also  feel  the  resistance  of  in- 
ertia. A  railroad  train,  for  example,  is  difficult  to  either 
start  or  stop  because  of  its  inertia.  A  ball  thrown  from 
the  hands  stops  only  because  of  the  pull  of  gravity  and 
the  resistance  of  the  air;  it  tends  to  go  on. 

Experiment. — Place  a  card  on  the  end  of  the  finger,  and  a  coin 
on  the  card.  Strike  the  card  lightly  out  of  its  place.  The  coin  will 
remain,  because  of  its  inertia. 

Porosity. — If  we  accept  the  molecular  theory,  all 
matter  is  porous.  We  usually  apply  the  term,  however, 
only  to  substances  in  which  the  quality  is  marked. 

Experiment. — Take  a  quantity  of  loose  absorbent  cotton,  and 
put  it  piece  by  piece  into  a  small  tumblerful  of  alcohol;  nearly  a 
quart  can  be  put  into  the  alcohol  before  the  tumbler  overflows. 
This  is  due  to  the  porosity  of  both  alcohol  and  cotton.  Examine 
the  stone  filter  from  a  water-sterilizing  apparatus;  one  would  say 
that  it  is  not  porous  at  all,  yet  water  goes  through  it  if  under  pres- 
sure. 

Porosity  involves  compressibility.  All  substances  are 
compressible,  but  in  varying  degrees;  it  is  merely  a 
question  of  applying  sufficient  force  to  drive  the  mole- 
cules closer  together.  Air  and  all  gases  are  readily 
compressible.  Some  solids  are.  Liquids  are  hardly 
compressible  at  all. 


MATTER.    ITS  COMPOSITION  27 

Elasticity  is  a  quality  which  substances  possess  in 
varying  degrees.  Some  return  to  their  original  shape 
and  size  when  compressed,  some  do  to  an  extent,  some 
not  at  all.  Some  substances  are  rapidly  elastic,  some 
slowly. 

SPECIFIC  QUALITIES 

There  are  numerous  special  qualities,  those  possessed 
only  by  certain  substances. 

Hardness  occurs  in  varying  degrees.  Lead  and  wood 
seem  hard,  but  may  be  easily  cut.  The  diamond  is 
the  hardest  known  substance. 

Opacity,  the  quality  which  prevents  light  from  passing 
through  a  substance,  and  transparency,  the  quality 
which  permits  its  passage,  are  important  qualities  which 
vary  greatly  in  different  sorts  of  matter. 

Tenacity,  that  is,  the  ability  to  keep  its  particles  to- 
gether, varies  greatly  in  different  substances.  Its  op- 
posite is  brittleness.  Important  manifestations  of  te- 
nacity are:  malleability,  the  quality  which  permits  a  sub- 
stance to  be  hammered  into  thin  sheets,  and  ductility, 
the  quality  which  permits  it  to  be  drawn  out  into  fine 
threads.  For  example,  gold  may  be  beaten  into  sheets 
4000000  inch  in  thickness,  or  so  thin  that  1  ounce  will 
cover  100  square  feet.  Platinum  is  extremely  ductile, 
but  the  finest  thread  we  know  is  that  of  the  spider's 
web;  this  is  used  in  some  scientific  apparatus  (the  mi- 
croscope, surveying  instruments)  because  no  artificial 
thread  is  so  fine. 


28  PRACTICAL  PHYSICS  FOR  NURSES 

Tendency  to  crystallize  is  a  property  of  nearly  all 
solid  substances.  Under  favorable  circumstances  most 
substances  tend  to  arrange  themselves  in  the  form  of 
crystals. 

Experiment. — Make  a  tumblerful  of  a  saturated  solution  of 
alum,  hot.  Hang  in  it  a  circle  of  wire  or  stiff  string  and  leave  it 
overnight  or  longer;  the  circle  will  be  covered  with  crystals. 

When  water  crystallizes,  in  freezing,  the  crystals  require  more 
room  than  the  liquid  and  insist  upon  expanding;  this  is  the  reason 
that  water-pipes  burst  when  they  freeze. 

FORMS  OF  MATTER 

Original  Forms  of  Matter. — Matter  exists  normally 
in  three  forms:  solid,  liquid,  and  gas. 

These  forms  are  due  to  the  weakness  or  strength  of 
the  force  of  cohesion  between  their  molecules.  Solids 
have  their  molecules  close  together  and  are  held  firmly; 
in  liquids  the  molecules  are  farther  apart  and  are  held 
loosely;  in  gases  they  are  still  farther  apart  and  tend  to 
recede  from  each  other. 

We  think  of  these  three  forms  as  characteristic  of 
certain  substances  themselves,  whereas,  in  reality,  they 
depend  entirely  upon  temperature. 

Change  of  Form. — Water  is  the  best  example  of  a 
substance  which  can  be  converted  into  the  form  of  a 
solid,  liquid,  or  gas.  The  same  changes  are  possible  in 
all  substances,  but  with  many  the  change  is  difficult  to 
accomplish,  and  in  some  cases  we  have  not  yet  learned 
how  to  do  it  without  damage.  For  example,  iron  can 
be  liquefied  by  applying  a  very  high  temperature;  it  may 


MATTER.    ITS  COMPOSITION  29 

also  be  vaporized,  but  it  takes  an  incredible  degree  of 
heat  to  accomplish  it.  Sugar  is  an  example  of  a  solid 
substance  which,  if  carefully  heated,  may  be  changed  to 
a  liquid.  Air,  which  we  think  of  as  a  gas,  can  be  made 
liquid  by  an  extreme  degree  of  cold;  and  it  has  even 
been  changed  into  a  solid  mass  by  still  greater  cold. 

Diffusion. — Solids  may  be  diffused — i.  e.,  the  molecules 
driven  farther  apart — (1)  by  melting;  (2)  by  solution; 
(3)  by  dialysis. 


Fig.  I.— Dialyzer  (Bliss  and  Olive). 

In  dialysis,  the  given  mixture  is  placed  in  a  small 
jar  having  a  parchment  paper  bottom;  this  is  set  into 
a  jar  of  pure  water.  Any  crystalloid  substance  will 
soak  out  through  the  parchment  into  the  water,  where 
its  presence  may  be  discovered  by  chemical  tests.  This 
method  is  used  for  examining  stomach  contents  in  cases 
of  suspected  poisoning.  It  is  not  applicable  to  colloid 
substances. 


30  PRACTICAL  PHYSICS  FOR  NURSES 

BRANCHES  OF  PHYSICS 

Mechanics  is  the  branch  of  physics  which  deals  with 
solid  bodies  and  the  laws  that  govern  them. 

Hydraulics  is  the  branch  which  deals  with  liquids  and 
the  laws  that  govern  them. 

Pneumatics  is  the  branch  which  deals  with  gases  and 
the  laws  that  govern  them. 

All  three  of  these  branches  of  science  apply  to  daily 
life,  to  the  human  body,  and  to  nursing. 

SUMMARY 

Physics  is  the  science  of  every-day  life.  It  treats  of 
matter,  its  properties,  changes,  and  motions.  A  knowl- 
edge of  it  is  necessary  in  order  to  deal  satisfactorily  with 
household  or  hospital  appliances,  and  for  a  correct 
understanding  of  the  human  body  and  its  functions. 

Substances  are  simple  or  complex,  i.  e.,  composed  of 
one  or  several  elements. 

The  Atomic  Theory  has  been  accepted  because  it 
accounts  for  all  natural  phenomena.  It  assumes  that 
all  matter  is  composed  of  molecules  (the  smallest  por- 
tions of  matter  that  can  exist  alone),  which  are  them- 
selves composed  of  atoms  (the  smallest  portions  of  mat- 
ter that  can  exist  in  combination).  Physics  concerns 
itself  with  molecules.  Chemistry,  a  branch  of  physics, 
concerns  itself  with  atoms. 

A  physical  change  is  the  change  in  the  form  of  a  sub- 
stance. 


MATTER.    ITS  COMPOSITION  31 

A  chemical  change  is  the  change  in  the  composition 
of  a  substance. 

Neither  atoms  nor  molecules  are  in  actual  contact 
with  each  other.  Atoms  are  held  together  by  chemical 
affinity;  molecules  of  the  same  sort  by  cohesion;  mole- 
cules of  different  sorts  by  adhesion. 

The  general  properties  or  characteristics  of  matter 
are  extension,  divisibility,  mobility,  inertia,  porosity, 
compressibility,  etc. 

Some  of  the  specific  properties  of  matter  are  hardness, 
opacity,  transparency,  tenacity,  brittleness,  tendency 
to  crystallize,  etc. 

Matter  exists  in  three  forms — solid,  liquid,  and  gas. 
These  forms  are  due  to  the  strength  or  weakness  of  co- 
hesion between  their  molecules.  This  depends  upon 
their  temperature,  which  is  a  relative  matter.  As  a 
rule,  low  temperatures  cause  matter  to  solidify,  high 
temperatures  cause  it  to  liquefy,  still  higher  cause  it  to 
become  gaseous. 

Mechanics  is  the  science  of  solids.  Hydraulics  is 
the  science  of  liquids.  Pneumatics,  the  science  of  gases. 


CHAPTER  II 
MECHANICS 

LAWS  RELATING  TO  SOLIDS 

Gravity  is  the  force  which  the  earth  exerts  on  all 
sorts  of  matter.  The  earth  pulls  everything— solids, 
liquids,  or  gases — toward  its  center.  This  pull  is  exerted 
in  a  straight  line,  directly  to  the  center  of  the  earth. 
It  is  called  the  "line  of  direction."  The  exact  direction 
of  this  pull  is  shown  by  the  plumb  line  used  by  builders, 
artists,  etc.  A  building  which  is  "out  of  plumb"  is 
likely  to  fall  sooner  or  later,  since  the  foundation  may 
be  unable  to  hold  the  top  against  the  pull  of  the  earth. 

It  is  this  pull  of  the  earth  which  causes  objects  to 
fall  when  not  supported,  makes  the  rain  and  snow  de- 
scend, water  to  run  down  hill,  etc. 

Weight. — Another  manifestation  of  the  pull  of  the 
earth  is  what  we  call  weight.  Since  the  earth  pulls 
equally  on  every  molecule,  it  give  us  a  convenient  method 
of  finding  out  the  quantity  of  matter  in  a  mass.  Weight 
may  be  denned  as  the  measure  of  the  force  of  gravity 
upon  an  object. 

We  must  distinguish  clearly  between  amount  of  matter, 
which  refers  to  the  number  of  molecules  in  it;  and 
volume,  which  refers  to  the  space  it  occupies.  There 
is  the  same  amount  of  matter  in  a  pound  of  lead  and  a 


MECHANICS  33 

pound  of  feathers,  but  there  is  a  very  great  difference 
in  the  volume  of  the  two.  Weight  indicates  the  amount 
of  matter,  but  has  no  relation  to  volume. 

The  specific  gravity,  or  specific  weight,  of  any  sub- 
stance is  its  weight  as  compared  with  an  equal  volume 
of  some  substance  taken  as  a  standard.  In  the  case  of 
solids  and  liquids  water  is  used  as  the  standard  (dis- 
tilled water  at  a  temperature  of  4°  C.);  with  gases,  hy- 
drogen gas  at  0°  C.  For-  example,  water  is  called 
1.000.  Gold  is  19.5  (meaning  that  it  is  19|  times  as 
heavy  as  an  equal  volume  of  water);  copper  is  8.788; 
coal,  1.270;  urine,  about  1.020;  olive  oil,  .970;  alcohol, 
.797;  ether,  .734;  wood,  .580;  cork,  .240,  and  so  on. 


Fig.  2. — Center  of  gravity. 

The  Center  of  Gravity  of  an  object  is  the  point  on 
which  it  will  just  balance  itself,  no  matter  in  what 
position  it  is  placed.  It  is,  to  state  it  differently,  the 
weight  center  of  the  object. 


34 


PRACTICAL  PHYSICS  FOR  NURSES 


Equilibrium  is  poise  or  balance  between  two  or  more 
forces.  It  causes  a  body  to  remain  stable  when  there 
are  forces  tending  to  move  it. 

The  stability  of  an  object  depends  upon  the  relation 
of  its  center  of  gravity  to  its  base.  A  large  base  or  a 
low-down  center  of  gravity  gives  a  greater  stability. 

There  are  three  sorts  of  equilibrium :  (a)  Stable  when 
a  body  has  a  broad  or  heavy  base  and  a  low  center  of 


Fig.  3.  —  Stable  and  unstable  equilibrium. 


gravity.  Examples,  a  cone  or  pyramid,  a  chair  with 
four  spreading  legs,  a  quadruped.  (6)  Unstable,  when 
a  slight  force  will  push  an  object  over,  that  is,  when 
its  center  of  gravity  is  high  up  or  falls  toward  one  side 
of  the  base.  Examples,  a  book  standing  on  edge,  a 
biped;  extreme  examples,  a  person  standing  on  one  leg, 
a  tight-rope  walker,  (c)  Neutral,  when  a  slight  force 
would  not  act  upon  it,  nor  change  its  center  of  gravity. 
Example,  a  three-legged  stool,  which  stands  well  until 
a  heavy  weight  is  put  upon  one  side  of  it,  bringing  the 
center  of  gravity  outside  of  the  base. 
Standing  and  Walking.  —  Learning  to  stand  or  walk  is 


MECHANICS  35 

difficult  because  in  the  human  body  the  center  of  gravity 
is  high  up  from  the  ground  (in  the  abdomen),  and  the 
base  (the  space  enclosed  by  the  feet)  is  small  in  pro- 
portion. Standing  is  the  process  of  maintaining  one- 
self in  equilibrium  on  a  small  base.  Walking  is  a  proc- 
ess of  alternately  falling  forward  and  saving  oneself, 
the  center  of  gravity  being  thrown  first  over  one  foot, 
then  over  the  other.  When  one  carries  a  load  on  his 
back  he  bends  forward  so  as  to  have  the  center  of  gravity 
well  inside  his  base;  in  carrying  a  weight  in  the  hand  he 
bends  to  one  side  for  the  same  reason. 

Both  standing  and  walking  are  accomplished  by  the 
combined  action  of  many  muscles,  corresponding  sets 
on  each  side  pulling  against  each  other  to  stiffen  the 
framework  and  maintain  it  erect,  while  other  muscles 
are  moving  a  portion  or  the  whole.  The  processes  are 
exceedingly  complex,  and  it  is  not  surprising  that  it 
takes  some  months  to  acquire  them. 

In  using  a  cane  or  crutches  one  enlarges  his  base, 
thereby  making  his  equilibrium  more  stable. 

ENERGY.     WORK 

Whenever  anything  happens,  or  is  done,  there  is  some 
driving  force  behind  it.  This  driving  force  is  what  we 
call  energy.  There  are  various  sorts  of  energy,  heat 
being  the  commonest;  others  are  light  energy,  sound 
energy,  muscular  energy,  electric  energy,  chemical 
energy,  etc.  All  these  bring  about  changes  in  matter. 


36  PRACTICAL  PHYSICS  FOR  NURSES 

One  form  of  energy  may  be  changed  into  another,  as 
chemical  action  may  produce  heat,  motion  may  produce 
heat,  electricity  may  produce  light,  etc.  All  sorts  of 
methods  and  appliances  have  been  devised  to  ac- 
complish such  changes. 

Energy  is  Indestructible. — It  may  change  from  one 
form  to  another,  but  none  of  it  is  lost.  When  it  dis- 
appears at  one  spot,  it  reappears  at  another.  This  is 
called  the  law  of  conservation  of  energy.  Examples: 
coal  (stored-up  energy  derived  primarily  from  the  sun) 
is  burned,  producing  heat,  which  in  its  turn  produces 
steam,  which  in  its  turn  produces  motion,  which  may  be 
utilized  in  various  ways;  energy  used  in  winding  a  clock 
reappears  in  the  movements  of  the  clock;  electricity  may 
be  converted  into  sound  by  means  of  the  mechanism  of 
a  bell.  Many  examples  will  occur  to  anyone. 

Work. — Whenever  any  of  the  forms  of  energy  mani- 
fest themselves,  work  is  done. 

Whenever  work  is  done,  it  means  that  an  opposition 
of  some  sort,  a  resistance,  is  overcome,  and  some  change 
in  condition  results.  This  change  may  be  motion  or 
any  other  form  of  action. 

WORK  AND  MOTION 

Whenever  force  produces  motion,  work  is  done. 
This  amount  of  work  is  measured  by  the  distance  through 
which  a  body  is  moved  multiplied  by  the  force  which 
moves  it. 


MECHANICS  37 

The  fundamental  laws  of  motion  are  those  formulated 
by  Sir  Isaac  Newton.  They  are  as  follows: 

1.  A  moving  body  always  follows  a  straight  line,  unless 
it  is  acted  upon  by  another  force  which  changes  its  direc- 
tion. A  stone  dropped  from  a  height  moves  in  a  straight 


a  b 

Fig.  4. — a,  Cream  separator;  b,  detail  of  mechanism. 

line  because  it  is  acted  upon  by  but  one  force,  that  of 
gravity.  A  ball  thrown  from  the  hand  moves  in  a 
curve  because  it  is  being  acted  upon  by  two  forces,  the 
muscular  energy  which  started  it  and  the  pull  of  the 
earth;  the  resultant  of  the  two  forces  determines  its  path.1 
1  In  neither  case  do  we  take  into  account  the  resistance  of  the  air. 


38  PRACTICAL  PHYSICS  FOR  NURSES 

Centrifugal  Force. — Swing  a  weight  around  by  a  thread; 
one  is  conscious  that  it  is  trying  to  fly  off  in  a  straight 
line,  but  is  held  by  the  thread;  therefore  it  moves  in  a 
circle;  if  the  thread  breaks,  it  flies  in  a  straight  line  un- 
til pulled  toward  the  earth  by  gravity.  This  tendency 
of  a  moving  body  to  flee  from  a  fixed  center  is  called 
centrifugal  force  (from  centrum,  center,  and  fugere,  to 
flee,  Latin).  The  cream  separator  comes  under  this 
law.  The  milk  is  whirled  rapidly  and  tends  to  fly  into 
space,  but  is  held  back  by  the  container.  Cream  and 
skimmed  milk  being  of  different  densities,  they  separate 
in  the  whirling,  the  milk  going  to  the  outer  part  of  the 
container,  the  cream  remaining  nearer  the  center.  The 
urine  centrifuge  works  upon  the  same  principle,  the 
lighter  fluid  being  whirled  to  the  outside,  the  heavier 
sediment  remaining  at  the  center. 

2.  Every  change  in  motion  is  in  proportion  to  the  force 
or  forces  applied,  and  lakes  places-  in  the  straight  line  in 
which  that  force  (or  forces)  act. 

3.  To  every  action  there  is  always  an  equal  and  op- 
posite reaction.    This  principle  of  rebound  is  important 
and  should  be  borne  constantly  in  mind.     Surprisingly 
enough,  it  has  a  counterpart  in  the  realm  of  psychology; 
one  notes  how  depression  invariably  follows  excitement. 

MACHINES 

Machines  are  devices  by  which  work  may  be  done  more 
conveniently  or  advantageously  than  without  them. 
Man's  hands  are  unsuited  to  many  processes,  so  he  calls 


MECHANICS  39 

things,  or  combinations  of  things,  to  his  aid.  A  pencil 
is  a  machine,  strictly  speaking,  because  it  enables  us  to 
do  easily  what  would  otherwise  be  very  troublesome. 

Machines  convert  a  small  force  acting  through  a  long 
distance  into  a  great  force  acting  through  a  small  distance, 
or  vice  versa.  In  the  first  case  we  obtain  greater  power; 
in  the  second,  we  obtain  greater  exactness. 

Machines  enable  us  to  do  things  which  without  them 
would  be  too  large  for  us,  too  rapid  for  us,  or  too  exact 
for  us,  to  accomplish. 

The  body  is  sometimes  referred  to  as  "the  human 
machine."  This  is  in  a  sense  correct,  since  many 
parts  of  it  are  constructed  like  other  machines,  and 
portions  literally  are  machines. 

The  Driving  Force. — A  machine  does  not,  by  itself, 
literally  do  the  work  demanded  of  it.  There  must 
always  be  a  driving  force,  and  it  is  this  which  in  reality 
does  the  work.  The  machine  is  that  through  which  the 
driving  force  acts. 

Our  most  interesting  and  useful  machines  are  those  in 
which  the  power,  or  driving  force,  is  some  other  than  our 
own.  Some  machines  are  driven  by  horse  power  or 
the  energy  of  other  animals;  some  run  by  the  forces  of 
nature,  as  wind  or  water;  steam  engines  use  the  energy 
stored  up  in  coal;  motor  cars  utilize  that  stored  in  gaso- 
line; electric  appliances  make  use  of  the  power  obtained 
from  electricity,  which  may  in  its  turn  be  derived  from 
some  other  source  of  energy. 

Types  and  Classes  of  Machines. — Machines  are  of 


40  PRACTICAL  PHYSICS  FOR  NURSES 

two  general  types  and  are  divided  into  six  classes. 
The  lever,  the  -wheel  and  axle,  and  the  pulley  are  of  one 
type;  the  inclined  plane,  the  wedge,  and  the  screw  are  of 
the  other  type. 

SUMMARY 

Gravity  is  the  force  by  which  the  earth  pulls  everything 
toward  its  center.  Its  action  produces  weight,  which 
enables  us  to  know  the  amount  of  matter  in  any  given 
mass  or  object. 

Specific  gravity  is  the  weight  of  any  given  substance 
compared  with  water  as  a  standard. 

Equilibrium,  the  balance  between  two  or  more  forces, 
may  be  stable,  unstable,  or  neutral.  Man,  in  walking 
upright,  is  in  a  state  of  unstable  equilibrium,  as  his 
base  is  small  and  his  center  of  gravity  high  up. 

The  driving  force  behind  any  action  is  called  energy. 
There  are  various  forms  of  energy,  light,  heat,  chemical, 
muscular,  electric,  etc.  One  form  of  energy  may  be 
changed  into  another,  but  none  is  ever  lost  or  destroyed. 

Manifestations  of  energy  are  called  work.  This  is 
an  overcoming  of  resistance  or  some  change  in  condition. 

Newton's  three  laws  of  motion  cover  the  fundamentals. 

Machines  are  devices  by  means  of  which  we  may  ac- 
complish things  otherwise  too  large,  too  rapid,  or  too 
exact  for  us  to  do  unaided. 

Behind  the  machine  there  must  always  be  a  driving 
force,  such  as  that  supplied  by  the  strength  of  animals, 
by  water-power,  wind,  electricity,  gasoline,  coal,  etc. 

There  are  six  classes  of  machines. 


CHAPTER  III 

. 

MECHANICS  (Continued) 

THE  lever  is  the  most  common  and  most  useful  ma- 
chine; in  fact,  nearly  all  machines  are,  in  a  sense,  va- 
rieties of  lever  or  combinations  of  levers. 

A  lever  is  a  rigid  bar,  straight  or  curved,  resting  on  a 
fixed  point  or  edge,  called  the  fulcrum.  It  is  used  to 
move  weight  or  overcome  resistance.  The  hand-spike 
is  a  common  form  of  the  simple  lever. 

There  are  three  things  concerned  in  the  action  of  a 
lever:  1.  The  weight  to  be  lifted  or  moved.  2.  The 
power  which  shall  move  it.  3.  The  fulcrum,  or  point 
upon  which  the  movement  is  to  take  place. 

There  are  three  classes  of  levers:  In  the  first  class  the 
fulcrum  is  between  the  weight  and  the  power.  In  the 
second  class  the  weight  is  between  the  fulcrum  and  the 
power.  In  the  third  class  the  power  is  between  the 
fulcrum  and  the  weight. 

In  all  cases  it  is  possible  to  calculate,  by  mathematical 
means,  the  exact  power  that  will  be  required  to  move  a 
given  weight  through  a  given  distance. 

In  levers  of  the  first  class,  the  fulcrum  being  between 
the  power  and  the  weight,  the  weight  moves  in  an  op- 
posite direction  to  that  in  which  the  power  is  applied.  Com- 

41 


42  PRACTICAL  PHYSICS  FOR  NURSES 

mon  examples  are  the  tack  lifter,  the  can  opener,  the 
pump  handle,  the  grocer's  scales,  etc. 


II 


III 


-A. 

Fig-  5- — The  three  classes  of  lever. 

Scissors,  pliers,  artery  clamps,  etc.,  are  double  levers 
of  the  first  class,  the  weight  being  between  the  blades, 


MECHANICS 


43 


the  power  the  force  applied  by  the  hand,  the  fulcrum 
the  joint.  The  bivalve  speculum  is  a  double  lever,  the 
weight  being  the  walls  of  the  cavity  into  which  it  is  in- 


Fig.  6.— Levers  of  the  first  class:  A,  Uterine  dilator;  B,  can  opener; 
C,  claw  hammer;  D,  chisel.     (Butler,  "Household  Physics.") 


44  PRACTICAL  PHYSICS  FOR  NURSES 

serted.  The  long  uterine  dilator  with  two  handles  is 
also  a  double  lever.  (The  small,  graduated  dilators  are 
wedges,  not  levers.) 

If  the  power  arm  of  the  lever  is  long  and  the  weight 
arm  short,  the  work  is  more  easily  done  than  if  the  re- 
verse is  the  case;  the  distance  an  object  can  be  moved 
in  this  case  is  lessened,  but  force  and  time  are  gained. 


Fig.  7. — Levers  of  the  first  class,  with  long  and  short  power 
arms:  a,  Paper-cutting  shears;  b,  metal-cutting  shears.  (Butler, 
"Household  Physics.") 

In  the  large  uterine  dilator  great  force  is  gained  because 
of  the  excessive  length  of  the  handles.  It  is  for  this 
reason  that  metal-cutting  shears  have  long  handles, 
while  scissors  for  cutting  paper  have  very  short  handles; 
the  first  requires  great  power;  the  second,  little  power 
but  a  long  sweep. 

In  the  human  anatomy  there  are  many  portions  which 
can  be  used  as  levers  of  the  first  class.  In  grasping  an 
object  with  the  hand,  the  object  is  the  weight,  the 
ringer  joints  are  the  fulcrum,  the  flexor  muscles  the 
power.  In  putting  the  head  back  the  joint  at  the  top 
of  the  spine  is  the  fulcrum,  the  head  is  the  weight,  and 
the  muscles  at  the  back  of  the  neck  are  the  power 


MECHANICS 


45 


(see  Fig.  11).  In  pushing  an  object  with  the  foot,  the 
object  is  the  weight,  the  ankle-  or  knee-joint  is  the  ful- 
crum, the  leg  muscles  the  power. 


AF 


Fig.  8. — Levers  of  the  second  class:  a,  Nut-cracker;  b,  wheelbarrow. 
(Butler,  "Household  Physics.") 

In  levers  of  the  second  class  the  weight  being  be- 
tween the  power  and  the  fulcrum,  the  weight  moves  in 


Fig-  9- — Levers:  a,  Jaw  of  human  being;  b,  foot  when  we  rise  on  the 
toes.     (Butler,  "Household  Physics.") 

the  same  direction  as  that  in  which  the  power  is  applied. 
The   wheelbarrow   is   a   common    example.    The   nut 


46 


PRACTICAL  PHYSICS  FOR  NURSES 


cracker  and  the  lemon  squeezer  are  double  levers  of 
the  second  class. 


Fig.  10. — Levers  of  the  third  class:  a,  Sugar  tongs;  b,  fork;  c, 
forearm;  d,  spoon,  knife,  potato  masher,  pliers,  wrench,  and  fire 
tongs.  (Butler,  "Household  Physics.") 


MECHANICS  47 

In  lifting  the  weight  of  the  body  to  the  tip-toes,  the 
toes  form  the  fulcrum,  the  calf  muscle  the  power. 

In  this  class  of  lever  also,  if  the  weight  is  near  the  ful- 
crum, and  the  power  arm  is  long,  the  work  is  more  easily 
accomplished. 

In  levers  of  the  third  class  the  fulcrum  is  at  one  end, 
the  weight  at  the  other,  the  power  between  them.  Com- 
mon examples  are  the  fork  and  spoon,  as  used  in  eating. 
Sugar  tongs  and  thumb  forceps  are  double  levers  of  the 
third  class. 

It  will  readily  be  seen  that  this  form  of  lever  is  not  of 
advantage  in  lifting  weights,  since  the  power  must  always 
be  greater  than  the  weight  to  be  lifted.  It  is  used 
chiefly  when  we  wish  to  produce  a  rapid  motion  through 
a  considerable  distance,  or  to  facilitate  small,  exact 
movements. 

The  flexing  of  the  forearm  constitutes  a  lever  of  the 
third  class.  The  weight  is  the  hand  and  anything  it 
may  contain,  the  fulcrum  is  the  elbow-joint,  the  power 
is  the  biceps  muscle,  applied  at  its  point  of  attachment 
below  the  elbow.  It  is  clear  that  this  is  not  designed 
for  the  lifting  of  great  weights,  but  for  quick,  dextrous 
movements. 

The  bending  of  the  head  forward  is  done  by  a  leverage 
of  the  third  class;  the  sternomastoid  muscle  is  the 
power,  the  sternoclavicular  attachment  the  fulcrum, 
the  head  the  weight. 

Another  example  is  the  use  of  the  lower  jaw  in  masti- 


48 


PRACTICAL  PHYSICS  FOR  NURSES 


cation.  The  weight  or  resistance  is  the  food  between 
the  teeth,  the  fulcrum  is  the  articulation  near  the  ear, 
the  power  is  the  masseter  muscle. 

Complicated  Movements. — Most  of  the  movements 
of  the  body  are  complicated,  two  or  more  fulcrums  and 
a  number  of  muscles  being  brought  into  play.  (This  is 
also  true  of  a  great  many  machines.)  We  commonly 


Fie.  ii. — Muscles  of  neck  as  levers  (Dorland's  Dictionary). 

lift  a  heavy  object  by  using  the  muscles  of  the  shoulders 
and  back,  somewhat  assisted  by  those  of  the  arm,  the 
elbow  and  shoulder-joints  being  the  fulcrums,  and  the 
action  being  a  combination  of  Wers  of  the  first  and  third 
classes. 

An  example  of  a  powerful  double  lever  is  observed 
when  the  body  is  raised  from  a  squatting  position. 
The  knee-joints  are  the  fulcrums,  the  power  is  the  leg 


MECHANICS 


49 


muscles.     In  machinery  such  an  arrangement  is  called 
the  toggle-joint  or  Stanhope  lever. 

OTHER  MACHINES 

The  crank-and-axle  (or  wheel-and-axle)  is  a  variety 
of  lever,  a  sort  of  continuous  lever.  Common  examples 
are  the  coffee-mill,  the  clothes-wringer,  the  bread-mixer, 


Fig.  12. — The  crank  and  axle:    a,  Treadle  of  sewing  machine;  b, 
bread  mixer.     (Butler,  "Household  Physics.") 

the  Dover  .egg-beater,  the  ice-cream  freezer,  etc.  The 
weight  is  the  material  to  be  acted  upon  or  moved,  the 
fulcrum  the  axle  or  bearing  upon  which  the  movement 
takes  place,  the  power  the  muscle  of  the  operator,  acting 
through  the  wheel  or  crank. 
The  driving  mechanism  of  a  sewing  machine  is  a 


5° 


PRACTICAL  PHYSICS  FOR  NURSES 


combination  of  the  wheel-and-axle  and  a  lever   (the 
treadle). 

The  pulley  consists  of  a  grooved  wheel  called  a  sheave, 
set  into  a  frame,  the  block;  the  weight  to  be  lifted  is  at- 
tached to  one  end  of  a  rope  which  runs  over  the  sheave, 


a  b 

Fig.  13. — The  pulley:  a,  Simple;  b,  compound. 

the  power  being  applied  at  the  other  end  of  the  rope. 
Adding  more  sheaves  multiplies  the  power,  so  that  very 
little  force  may  be  needed  to  move  a  considerable  weight. 
The  extension  apparatus  used  in  fractures  of  the 
thigh  is  a  simple  pulley,  the  weight  being  the  body  of 
the  patient,  the  power  being  the  weights  attached  at 


MECHANICS  51 

the  foot  of  the  bed.  The  action  is  not  movement, 
but  merely  pull.  The  superior  oblique  muscle  of  the 
eye  is  a  pulley,  also  the  omohyoid  muscle. 

The  inclined  plane  needs  little  explanation,  it  being 
obvious  that  a  weight  can  be  pushed  or  pulled  up  an 
incline  with  much  less  effort  than  it  can  be  lifted  verti- 
cally to  the  same  height. 

•  P 


Fig.  14. — The  inclined  plane. 

A  series  of  rules  have  been  formulated  by  which  one 
may  calculate  the  exact  force  necessary  to  move  a  given 
weight  up  an  incline  of  a  given  angle. 

The  screw  is  a  curved  inclined  plane.  It  is  com- 
monly used  to  increase  the  pressure  of  one  object  upon 
another,  usually  with  the  purpose  of  holding  one  or  both 
in  place.  It  is  also  used  to  produce  a  small,  very  exact 
adjustment.  The  adjusting  mechanism  of  the  micro- 
scope is  an  example  of  how  a  screw  changes  a  long  move- 
ment into  a  short,  exact  one. 

The  screw-driver  is  a  lever  which  assists  the  placing 
of  the  screw.  In  forms  of  screw  like  the  letter  press, 
the  beef-juice  press,  the  meat  grinder,  the  bread  slicer, 


52  PRACTICAL  PHYSICS  FOR  NURSES 

etc.,  the  handle  is  a  lever;  in  the  two  latter  the  handle 
is  a  modified  lever,  the  crank  and  axle. 

The  wedge  is  a  double  inclined  plane  which  is  forced 
in  between  two  surfaces  or  portions  of  matter  in  order 
to  separate  them  or  in  order  to  hold  them  against  re- 
sistance. The  power  used  is  applied  in  the  form  of 
blows  rather  than  as  a  continuous  push.  The  wedge 
is  a  very  powerful  machine. 


Fig.  15.— The  wedge. 

Knives  are  wedges  with  delicate  edges.  Rectal  di- 
lators and  the  small  uterine  dilators  are  round  wedges. 

The  mechanics  of  obstetrics  is  most  interesting, 
though  somewhat  complicated.  The  child  is  the  weight, 
and  the  tissues  of  the  cervix,  the  vagina,  and  perineum 
the  resistance  to  be  overcome.  The  muscles  of  the  ab- 
dominal wall  and  of  the  uterus  are  the  power.  If  the 


MECHANICS 


53 


woman  is  on  her  feet,  gravity  assists  the  process.  If  she 
is  in  bed,  additional  force  may  be  obtained  by  the  pull 
of  her  arm  and  leg  muscles  against  some  firm  objects. 

The  child's  head,  in  combination  with  the  sac  of 
amniotic  fluid  which  acts  as  a  cushion  to  prevent  in- 
jury to  the  tissues,  acts  as  a  wedge  to  force  the  tis- 


Fig.  16. — Child's  head  acting  as  wedge  (DeLee). 

sues  apart.  Note  how  the  power  is  applied  inter- 
mittently during  the  pains.  The  great  force  employed  is 
appreciated  by  anyone  who  has  actually  delivered  a  child. 
The  birth  canal  is  not  straight,  but  much  curved, 
being  about  one-third  of  a  circle.  It  is,  in  effect,  a 
series  of  inclined  planes,  which  in  succession  change 
the  direction  of  the  child's  progress. 


54 


JPRACTICAL  PHYSICS  FOR  NURSES 


If  the  natural  forces  are  not  sufficient  to  produce  the 
necessary  progress,  the  obstetric  forceps,  a  double  lever 


Fig.  17. — Diagram  showing  the  advancement  of  the  head  through 
the  pelvis  (Leishman). 


Fig.  18. — Forceps:  a,  Obstetric;  b,  axis-traction. 

of  the  first  class,  is  used  to  assist  the  process.    With 
them  the  obstetrician  holds  the  progress  that  has  been 


MECHANICS  55 

made,  or  aids  it  by  pulling  in  the  direction  that  the 
other  forces  are  pushing,  and  in  which  the  child's  head 
is  moving.  Since  the  passage  is  not  straight,  the  for- 
ceps must  be  curved,  and  the  pull  must  be  made  in  the 
direction  that  the  child's  head  is  traveling.  "Axis- 
traction"  forceps  enable  the  operator  to  get  his  pull  in 
the  proper  direction  while  the  head  is  still  far  up  and 
the  curve  is  very  great.  Watch  the  direction  taken  by 
the  handles  of  the  forceps  during  a  delivery  and  note  how 
great  a  curve  they  describe  during  the  descent  of  the 
child.  At  first  they  point  somewhat  downward,  and 
at  the  end  of  the  delivery  almost  upward. 

FRICTION 

When  the  surface  of  one  body  is  made  to  move  over 
that  of  another,  a  resistance  to  the  movement  is  felt. 
This  resistance  is  friction.  If  perfectly  smooth  surfaces 
could  be  obtained,  there  would  be  little  or  no  friction; 
but  this  is  impossible.  There  is  always  more  or  less 
roughness,  and  therefore  some  resistance.  Roughness 
increases  friction,  smoothness  reduces  it. 

Without  the  action  of  friction  we  should  find  it  ex- 
ceedingly difficult  to  hold  anything  in  place;  everything 
would  tend  to  slip  from  our  hands  or  slide  away  at  a 
touch.  Without  friction  we  should  be  unable  to  walk 
or  drive,  as  we  should  constantly  slip.  It  is  an  impor- 
tant factor  in  life. 

There  are  two  sorts  of  friction,  rolling  and  sliding. 


56  PRACTICAL  PHYSICS  FOR  NURSES 

The  former  gives  the  least  resistance.  In  machines  with 
which  we  wish  to  do  work  easily  we  make  use  of  smooth, 
rolling  surfaces,  since  they  move  with  greater  ease. 


Fig.  19. — Friction.     Sliding  and  rolling. 

The  so-called  ball-bearings,  where  there  are  a  number  of 
parts  which  roll  over  one  another,  produce  a  very 
easy-running  joint. 


CoronoicL— 


-Ulna* 


Fig.  20. — Construction  of  joint  (after  Toldt). 

On  the  other  hand,  a  brake  set  to  a  wheel  changes 
rolling  into  sliding  friction,  and  so  checks  the  motion. 

Lubricants  reduce  friction;  it  is  for  this  reason  that 
we  oil  or  grease  machinery. 


MECHANICS  57 

Great  friction  produces  heat  (see  page  98)  which  may 
interfere  markedly  with  the  action  of  a  machine. 

The  human  body  presents  very  perfect  examples  of 
reduction  of  friction.  The  joints  are  nearly  all  rolling 
joints,  rather  than  sliding,  thus  offering  the  least  re- 
sistance to  movement,  and  constitute  a  great  economy 
of  force  or  power.  The  cartilages  that  cover  the  working 
portions  of  the  joints  are  practically  perfect  in  their 
smoothness,  and  the  synovial  fluid  is  a  fine  and  perfect 
lubricant,  continually  renewed.  It  is  when  joints  are 
roughened  or  dried  by  disease  that  they  work  with 
difficulty. 

SUMMARY 

The  lever  is  one  of  the  most  used  of  mechanical  devices. 
There  are  three  essentials  to  its  -action — the  weight, 
the  power,  and  the  fulcrum  or  point  on  which  the 
motion  takes  place. 

There  are  three  classes  of  levers;  they  vary  according 
to  the  relative  positions  of  weight,  power,  and  fulcrum. 
Examples  of  each  sort,  may  be  found  among  appliances 
in  every-day  use,  and  in  muscular  actions  taking  place 
in  the  human  body. 

Many  of  the  body  movements  are  complicated,  being 
produced  by  the  combined  action  of  many  muscles,  and 
involving  two  or  more  joints  as  fulcrums. 

The  wheel-and-axle  is  a  continuous  lever.  It  is  used 
in  many  domestic  appliances. 


$8  PRACTICAL  PHYSICS  FOR  NURSES 

The  pulley  consists  of  a  sheave  set  into  a  block; 
over  this  runs  a  cord  attached  to  both  weight  and  power. 
A  pulley  with  several  sheaves  facilitates  the  moving  of 
a  weight. 

The  inclined  plane  is  another  machine  which  de- 
creases labor  in  the  lifting  of  weights. 

The  screw  is  a  curved  inclined  plane  with  a  rather 
complex  mechanism.  It  has  many  applications  in 
domestic  and  hospital  life. 

A  wedge  is  a  double  inclined  plane  driven  by  inter- 
mittent blows;  it  is  used  when  great  force  is  needed  to 
separate  or  hold  objects. 

Most  of  our  so-called  machines  are  complex  combina- 
tions of  two  or  more  of  the  simple  machines. 

An  obstetric  delivery  is  essentially  a  mechanical  proc- 
ess. The  child's  head  acts  as  a  wedge  to  overcome  the 
resistance  of  the  cervical,  vaginal,  and  perineal  tissues. 
The  force  employed  is  that  of  the  abdominal  and  uterine 
muscles;  it  may  when  necessary  be  aided  by  the  pull  of 
obstetric  forceps.  The  birth  canal  being  curved — prac- 
tically a  series  of  inclined  planes — the  shape  of  the 
forceps  and  the  direction  of  the  pull  must  correspond 
with  it. 

Friction  is  the  resistance  between  two  surfaces,  one 
of  which  moves  over  the  other.  It  is  inevitable,  since 
a  perfectly  smooth  surface  is  impossible  to  obtain.  It 
is  of  advantage  in  holding  or  placing  objects,  but  is  a 
disadvantage  when  we  wish  to  move  them.  Sliding 


MECHANICS  59 

friction  may  be  changed  to  rolling  friction,  and  therefore 
reduced,  by  the  use  of  lubricants. 

The  human  body  presents  many  excellent  examples  of 
the  advantages  of  the  reduction  of  friction. 


CHAPTER  IV 

HYDRAULICS 

LAWS  RELATING  TO  LIQUIDS 

Properties  of  Liquids. — Liquids  tend  to  keep  their 
molecules  together,  but  not  strongly.  The  force  of 
their  cohesion  is  not  enough  to  overcome  the  action  of 
gravity;  therefore  they  "run"  to  the  earth  unless  pre- 
vented by  other  forces. 

Different  liquids  possess  different  degrees  of  cohesion. 
We  note  this  in  the  varying  size  of  drops  of  different 
liquids.  Castor  oil,  for  example,  coheres  rather  strongly, 
and  its  drops  are  correspondingly  large.  Alcohol  has 
less  cohesive  force,  and  its  drops  are  smaller.  Chloro- 
form drops  are  very  small. 

(Sixty  drops  of  water  make  a  dram  by  measure.  Carbolic 
acid  takes  118  drops  to  make  a  dram;  tincture  of  aconite,  150; 
ether,  180;  chloroform,  240.) 

Liquids  are  very  much  less  compressible  than  solids;  in 
fact,  most  of  them  are  not  compressible  to  any  appreciable 
extent.  This  is  an  important  characteristic  in  their 
use  in  practical  life. 

Water  is  the  most  common  and  the  most  important 
liquid.  It  is  therefore  used  as  a  standard  for  measuring 
the  qualities  of  other  fluids.1 

1  Specific  gravity,  or  the  weight  of  a   substance   compared  with 
the  same  amount  of  water,  as  before  noted,  refers  to  both  liquids 
and  solids. 
60 


HYDRAULICS  61 

Liquids  vary  greatly  in  their  weight.  Note  the  dif- 
ference in  weight  of  equal-sized  bottles  of  oil  and  of 
sulphuric  acid.  A  cubic  foot  of  cold  water  weighs  62.42 
pounds.  In  hot  water  the  molecules  are  farther  apart, 
therefore  it  requires  a  little  more  space  and  weighs  a 
little  less. 


Fig.  21. — Water  pressure  on  bottom  of  container. 

Pressure  in  Liquids. — If  1  cubic  foot  of  water  is  placed 
on  top  of  another,  the  weight  is  124.84  pounds;  that  is, 
the  pressure  upon  the  bottom  of  the  container  is  that 
amount.  So,  if  water  is  5  feet  deep,  the  bottom  of  the 
container  must  bear  a  weight  of  more  than  300  pounds 
to  the  square  foot.  From  this  one  can  see  that  the 


62 


PRACTICAL  PHYSICS  FOR  NURSES 


pressure  in  deep  water  is  very  great.    It  is  for  this 
reason — the    great   pressure — that    sea    divers    cannot 


Fig.  22. — Irrigator  hung  high.    The  whole  column  of  water  makes 
pressure  (DeLee). 

go  to  any  great  depth;    and  they  must  always  wear 
suits  of  material  heavy  enough  and  stiff  enough  to  re- 


HYDRAULICS  63 

sist  the  weight  of  the  water  and  keep  it  from  crushing 
them. 

The  irrigators  which  we  use  in  hospital  work  also 
illustrate  the  pressure  of  fluids.  If  an  irrigator  is  hung 
high,  there  is  more  water  in  the  tube,  i.  e.,  it  is  deeper, 


Fig.  23. — Irrigator  hung  low.     There  is  very  little  pressure,  because 
the  depth  of  water  in  irrigator  and  tube  is  not  great  (DeLee). 

and  the  pressure  exerted  upon  its  lower  part,  upon  the 
small  surface  which  is  the  caliber  of  the  tube,  is  that  of 
the  whole  column  of  water  in  both  irrigator  and  tubing. 
If  hung  low,  there  is  very  little  pressure,  and  the  water 
when  released  finds  its  escape  easily  and  gently.  It 


64  PRACTICAL  PHYSICS  FOR  NURSES 

is,  we  observe,  the  depth  and  not  the  amount  of  water 
which  regulates  the  pressure  upon  the  bottom. 

Pascal's  law  formulates  another  important  fact. 
The  pressure  in  a  liquid  is  tlie  same  in  all  directions.. 
Solids  press  only  downward;  liquids  press  sideways 
and  upward  as  well. 

Experiments. — (a)  Fill  a  hot-water  bag  quite  full  of  water, 
getting  out  all  the  air;  lay  on  the  hand;  press  the  top  or  side  of  the 
bag  and  note  that  the  resistance  is  as  great  in  one  place  as  in  another. 
(b)  Let  water  run  from  an  irrigator  to  the  tubing  of  which  is  at- 
tached a  uterine  tip,  one  having  several  holes;  note  that  the  water 
runs  with  equal  force  from  all  of  the  holes,  not  more  forcibly  from 
the  bottom  hole,  as  one  would  expect. 

The  discomfort  of  a  patient  from  a  full  bladder  is  due 
to  this  law,  because  the  urine  is  pressing  in  all  directions. 

A  water-bed  is  useful  because  it  makes  pressure  upon 
the  surface  of  the  patient's  body  equally  in  all  places, 


Fig.  24. — Water-bed. 

unlike  the  ordinary  bed,  which  presses  harder  against 
the  more  prominent  portions. 

It  is  this  law  which  causes  the  force  of  the  heart-beat 
to  be  distributed  evenly  throughout  the  body,  so  that 
blood-pressure  is  the  same  in  all  arteries,  large  or  small, 
far  away  from  or  near  to  the  heart. 

It  is  this  law  which  makes  the  sac  of  amniotic  fluid  so 


HYDRAULICS  65 

efficient  yet  so  gentle  a  dilator  in  obstetric  cases.  It 
presses  in  every  direction  at  once,  yet  without  possi- 
bility of  injury  to  the  tissues. 

Water  Seeks  its  Own  Level. — Because  water  presses 
in  all  directions  it  runs  through  any  available  openings, 
and  stops  only  when  there  is  a  resistance  ahead  of  it 
equal  to  the  force  or  weight  behind  it. 

Our  city  water  systems  are  based  upon  this  law.  The 
source  of  supply  is  a  lake  or  river  higher  than  the  city, 
or,  failing  this,  the  water  is  pumped  up  to  a  reservoir 


Fig.  25. — Diagram  of  artesian  well. 

or  standpipe  situated  upon  high  ground.  (The  supply 
in  this  case  may  be  a  low  river,  a  spring,  a  well,  etc.) 
All  water  which  is  permitted  to  flow  from  this  reservoir 
or  source  of  supply  attempts  to  rise  as  high  as  its  origin. 
The  great  height  of  the  large  body  of  water  gives  us 
the  desired  pressure.  Water  coming  from  a  hose  used 
to  sprinkle  a  lawn  would  rise  to  the  top  of  the  water  in 
the  reservoir  from  which  it  flows  if  it  were  not  for  other 


66  PRACTICAL  PHYSICS  FOR  NURSES 

forces,  the  friction  against  the  inside  of  the  hose,  the  re- 
sistance of  the  air,  and  the  action  of  gravity. 

Artesian  wells  are  produced  by  water  trying  to  find 
its  level.  The  source  of  the  water  is  in  the  hills  that 
are  above  the  well;  the  water,  soaking  through  the 
earth  and  running  along  an  impervious  layer  of  rock  or 
clay,  finds  an  opening  and  pushes  up  through  it,  or, 
more  correctly,  is  pushed  up  through  it  by  the  body  of 
water  behind  it.  In  some  cases  artesian  wells  spout 
high  above  the  ground. 

Buoyancy. — Push  a  block  of  wood  under  water  and 
release  it;  it  rises  to  the  surface  and  floats  with  its  bulk 
almost  out  of  the  water.  This  is  due  to  the  buoyancy 
(not  of  the  wood,  but)  of  the  water,  i.  e.,  its  tendency 
to  raise  all  bodies  to  its  surface.  This  is  due  to  the  facts 
already  discussed,  that  pressure  increases  with  depth 
and  that  it  acts  in  all  directions.  This  results  in  the 
pressure  upward  on  the  bottom  of  a  submerged  object 
being  greater  than  the  pressure  downward  upon  its  top. 
If  the  additional  weight  of  the  body  itself  is  not  more  than 
this  difference  of  pressure  against  top  and  bottom,  the 
object  floats. 

Heavy  substances,  which  displace  less  than  their  own 
weight  of  water,  sink.  Light  substances,  which  dis- 
place more  than  their  weight,  float.  The  law  of  Archim- 
edes— a  floating  body  sinks  until  it  displaces  its  own 
weight  of  liquid — is  a  summary  of  the  above  facts  and 
other  similar  ones. 


HYDRAULICS  67 

Swimming. — The  human  body,  partly  because  of 
the  air  in  its  tissues  and  in  the  lungs,  is  but  slightly 
heavier  than  water,  so  that  it  floats  just  below  the  sur- 
face. With  slight  effort  a  portion  of  the  head — mouth, 
nose,  and  eyes — can  be  kept  above  the  water,  making 
it  possible  for  a  person  to  swim.  The  balance  is  so 
nearly  equal  that  it  takes  only  a  small  quantity  of  water 
getting  into  the  lungs  and  replacing  the  air  to  cause  one 
to  sink,  i.  e.,  drown.1 

Experiment. — A  fine  needle,  especially  if  dipped  in  oil,  can  be 
made  to  float  on  water  if  it  is  laid  gently  and  evenly  upon  the 
surface.  Its  weight  is  not  sufficient  to  overcome  the  force  of  the 
cohesion  of  the  molecules  of  water. 

Loss  of  Weight  in  Water. — On  account  of  this  quality 
of  buoyancy,  all  objects  weigh  less  in  water  than  they 
do  in  air.  The  water  pushes  up  or  sustains  a  con- 
siderable portion  of  their  weight.  Experiments  are 
easily  made  which  prove  this. 

Hydrometers. — The  hydrometer  is  a  device  used  for 
ascertaining  the  specific  gravity  of  liquids.  It  is  based 
upon  the  law  of  Archimedes.  It  consists  of  a  tube 
weighted  at  one  end  with  the  requisite  amount  of  mer- 
cury, and  marked  with  a  scale.  The  point  marked  0  is 
the  point  to  which  it  sinks  in  water.  Placed  in  a  liquid 

1  Bodies  of  drowned  persons  sometimes  float  after  being  in 
water  a  considerable  length  of  time.  This  is  because  chemical 
changes  have  taken  place,  producing  in  the  tissues  gases  that  are 
lighter  than  water. 


68 


PRACTICAL  PHYSICS  FOR  NURSES 


heavier  than  water,  it  tends  to  float;  in  a  liquid  lighter 

than  water,  it  sinks  deeply.  The  scale  is  arranged  so 
that  it  designates  the  specific 
gravity. 

The  urinometer  and  the 
cream  tester  are  hydrometers. 
The  urinometer  is  of  impor- 
tance because:  (1)  If  urine  is 
of  low  specific  gravity,  i.  e., 
nearly  that  of  water,  it  indi- 
cates that  not  enough  solid 
matter  is  being  eliminated 
from  the  body.  (2)  If  it  is 
of  high  specific  gravity,  there 
is  too  much  solid  matter, 
i.  e.,  not  enough  fluid  is  being 
taken,  or  some  abnormal  con- 
dition is  causing  the  elimina- 
tion of  materials  that  should 
remain  in  the  body. 

The  specific  gravity  of  nor- 
mal milk  is  1029.  If  the  cream 
tester  shows  it  lower  than  this, 
there  is  a  suspicion  that  water 

may  have  been  added.    Excess  of  cream  may  change  the 

test  somewhat. 


Fig.  26. — Hydrometers. 


HYDRAULICS  69 

CAPILLARITY 

Capillarity,  or  capillary  attraction,  is  the  quality  that 
causes  liquids  to  adhere  to  solids  in  opposition  to  the  force 
of  gravity.  Its  action  is  most  marked  in  fine  tubes  and 
in  porous  substances. 

Experiments.— Hang  a  wick  of  gauze  over  the  edge  of  a  tumbler 
half  full  of  water;  water  will  soon  be  dripping  from  the  outer  end 
of  the  wick.  Hang  up  a  cloth  so  that  its  lower  edge  or  corner 
dips  into  water;  the  whole  cloth  will  gradually  become  wet.  Dip 
the  corner  of  a  lump  of  sugar  into  coffee  or  cocoa;  the  whole  lump 
very  quickly  becomes  colored  with  the  fluid.  Place  a  white  carna- 
tion or  other  white  flower  for  a  few  hours  in  a  bottle  of  red  ink; 
the  ink  stains  it,  especially  along  the  veins. 

It  is  capillarity  which  causes  the  sap  to  rise  in  plants, 
since  they  have  no  circulatory  system.  It  is  this  force 
which  helps  the  small  blood-vessels  of  the  intestines,  the 
lacteals,  and  the  lymphatics,  to  absorb  liquid  nourish- 
ment from  the  intestinal  contents.  It  is  this  which 
makes  possible  the  capillary  circulation  and  the  flow 
of  blood  in  the  very  small  veins;  the  force  of  the  heart- 
beat pushes  the  blood  only  part  way  through  the  smallest 
vessels,  but  capillarity  assists  and  continues  the  process, 
especially  when  it  is  necessary  for  the  blood  to  ascend, 
in  opposition  to  gravity. 

It  is  capillarity  upon  which  we  depend  largely  in  our 
drainage  of  wounds.  Gravity,  of  course,  assists  the 
process,  but  a  gauze  wick  will  drain  even  though  the 
fluid  to  be  removed  must  go  upward.  Drainage  stops 
when  the  gauze  becomes  blocked  with  solid  particles. 


70  PRACTICAL  PHYSICS  FOR  NURSES 

Waterproofed  cloth  is  that  which  has  been  treated 
with  something  which  prevents  capillary  action. 

DIFFUSION 

Diffusion  is  the  force  that  makes  fluids  tend  to  mix 
when  they  are  brought  into  contact. 

Experiments. — Put  some  solution  of  blue  vitriol  in  the  bottom 
of  a  test-tube;  tip  the  tube  and  with  a  medicine-dropper  put  carefully 
on  top  of  it  a  layer  of  water;  left  undisturbed,  they  gradually  mix, 
till  the  whole  is  blue.  Put  milk  at  the  bottom  of  a  test-tube  and 
water  on  top;  watch  them  mix. 

Osmosis. — A  similar  process  takes  place  through  thin 
animal  or  vegetable  membranes.  It  is  called  osmosis. 
It  applies  only  to  solutions  of  crystalline  substances, 
however. 

Experiment. — Procure  a  pig's  bladder  or  other  thin  animal 
membrane;  put  some  colored  fluid  into  it — a  solution  of  potassium 
permanganate  is  good — and  hang  it  in  or  touching  some  water. 
The  colored  fluid  will  penetrate  the  membrane,  and  color  the  water, 
the  latter  exchanging  places  with  it. 

It  is  the  combination  of  this  force  with  capillarity 
which  makes  possible  the  absorption  of  stomach  and 
intestinal  contents.  Osmosis  occurs  rapidly  through  the 
stomach  wall.  Note  that  the  drinking  of  hot  water 
causes  diuresis  within  fifteen  or  twenty  minutes,  long 
before  the  fluid  could  have  reached  the  intestines;  it  is 
absorbed  directly  from  the  stomach.  Medicines  given 
in  hot  water  are  quickly  absorbed  and  an  effect  produced 
in  a  short  time.  Osmosis  effects  this  by  carrying  the 
medication  through  the  stomach  wall  into  the  circulation. 


HYDRAULICS  71 

When  a  saline  cathartic  is  given,  the  saline  matter 
absorbs  much  water  from  the  tissues  of  the  intestines, 
pulling  it  through  the  membrane  of  the  intestinal  wall; 
the  excess  of  fluid  so  obtained  produces  a  watery  or  very 
soft  bowel  movement. 

Edema. — We  find  that  osmosis  takes  place  toward 
the  more  concentrated  solution,  and  that  saline  substances 
increase  it.  When,  therefore,  in  certain  diseased  con- 
ditions the  kidneys  fail  to  eliminate  a  sufficient  quantity 
of  saline  material  from  the  body  and  it  accumulates  in 
the  tissues,  it  produces  an  osmosis  of  the  body  fluids 
and  we  have  the  condition  which  we  call  edema. 


SUMMARY 

Cohesion  is  not  strong  in  liquids,  therefore  they  are 
easily  affected  by  gravity.  Liquids  are  very  slightly 
compressible. 

It  is  the  depth  of  water  rather  than  the  amount  pres- 
ent which  determines  the  pressure  upon  the  bottom  of 
the  container.  This  law  is  illustrated  by  the  ordinary 
hospital  irrigator. 

The  pressure  in  a  liquid  is  the  same  in  all  directions. 
This  is  illustrated  by  the  fact  that  quality  of  pulse  is 
the  same  in  all  parts  of  the  body. 

Water  seeks  its  own  level.  City  water  systems, 
artesian  wells,  irrigators,  etc.,  illustrate  this  law. 

A  floating  body  sinks  until  it  displaces  its  own  weight 


72      .  PRACTICAL  PHYSICS  FOR  NURSES 

of  the  liquid.  This  law  governs  the  use  of  the  urinom- 
eter,  etc.,  and  explains  ability  to  swim. 

Capillarity  is  the  property  that  causes  liquids  to  rise 
in  small  tubes  and  other  restricted  places  in  opposition 
to  the  action  of  gravity.  It  is  this  force  which  aids  the 
capillary  circulation,  absorption  from  the  alimentary 
canal,  the  drainage  of  wounds,  etc. 

Waterproofing  is  the  prevention  of  capillarity. 

Diffusion  is  the  property  which  causes  liquids  to  mix 
when  they  are  brought  into  contact.  When  it  takes 
place  through  a  membrane  it  is  termed  "osmosis." 

Osmosis  is  especially  active  in  saline  solutions;  it 
takes  place  toward  the  more  concentrated  solution. 
This  explains  the  occurrence  of  edema  when  there  is 
faulty  elimination. 


CHAPTER  V 
PNEUMATICS 

LAWS  RELATING  TO  GASES 

Properties  of  Gases. — In  gases  the  molecules  are  con- 
siderably separated  and  have  no  cohesion;  in  fact,  they 
are  always  trying  to  get  farther  apart  and  fail  only  be- 
cause outside  forces  prevent  them. 

Experiment. — Produce  dense  smoke  by  burning  sugar  or  setting 
fire  to  "touch-paper"  (unsized  paper  soaked  in  a  strong  solution  of 
saltpeter  and  dried).  The  smoke  quickly  becomes  diffused  through 
the  room,  even  though  there  are  no  apparent  currents  of  air. 

The  law  of  diffusion  of  gases  corresponds  to  that  of 
liquids.  Gases  which  are  in  contact  tend  to  mix.  If  it 
were  not  for  this  law  we  should,  in  a  closed  room,  be- 
come quickly  surrounded  by  a  lake  of  impure  air  which 
we  should  be  compelled  to  rebreathe.;  this  is  prevented 
by  the  rapid  diffusion  of  gases,  and  by  the  fact  that  air 
is  so  readily  disturbed,  so  that  the  opening  of  a  door  or 
the  moving  of  an  object  in  the  room  keeps  the  air  "stirred 
up." 

Elasticity  of  Gases. — Gases,  because  of  the  tendency 
of  their  molecules  to  get  away  from  each  other,  are  very 
elastic.  Note  the  great  elasticity  of  the  air  confined  in 
an  air-cushion,  an  automobile  or  bicycle  tire.  Observe 

7? 


74  PRACTICAL  PHYSICS  FOR  NURSES 

the  rapidity  and  force  with  which  it  escapes  when  even" 
a  small  opening  is  made. 

Compressibility  of  Gases. — All  gases  are  compressible, 
most  of  them  to  a  very  marked  degree.  It  is  well  known 
that  a  large  quantity  of  oxygen,  compressed  air,  carbon 
dioxid,  etc.,  may  be  forced  into  a  tank. 

Illuminating  gas  is  collected  in  very  large  iron  tanks, 
the  weight  of  which  is  sufficient  to  hold  it  in  place.  The 
tank  is  set  in  a  deep  cistern  of  water,  through  which  the 
gas  passes  with  great  difficulty,  and  the  tank  rises  or 
falls  in  it  according  to  the  amount  of  gas  it  con- 
tains. Pipes  are  laid  from  this  tank;  the  weight  of 
the  tank  and  the  elasticity  of  the  gas  itself  force  it 
through  the  pipes  in  every  direction  and  with  an  even 
pressure. 

Air  is  the  Most  Important  Gas. — It  is  composed  of  a 
mixture  (not  a  combination)  of  two  gases,  nitrogen 
(four-fifths)  and  oxygen  (one-fifth).1  If  it  were  not  for 
the  constant  action  of  the  law  of  diffusion  of  gases  the 
air  would  be  an  irregular  mixture,  somewhat  like  marble 
cake,  with  spots  and  streaks  of  the  two  gases,  causing 
endless  inconvenience  and  danger. 

The  air  surrounds  the  earth,  but  is  not  very  deep  over 
its  surface,  about  50  miles.  There  is  probably  some 
air  as  far  up  as  200  miles,  but  at  a  distance  of  7  or  8 
miles  above  the  surface  it  is  very  rare,  i.  e.,  its  molecules 


1  There  is  also  a  small  amount  of  carbon  dioxid,  watery  vapor, 
and  of  various  impurities  in  minute  quantities. 


PNEUMATICS  75 

are  far  apart.  Man  has  never  been  more  than  about  5 
miles  (25,000  feet)  above  sea-level. 

Air  has  Weight. — Air  is  matter  and  all  matter  is  at- 
tracted by  the  earth.  In  the  case  of  air,  the  force  with 
which  the  molecules  try  to  get  away  from  each  other  is 
slightly  less  than  the  attraction  of  gravity.  The  weight 
of  air  is  1.28  ounces  per  cubic  foot. 

Some  gases  are  lighter  than  air,  some  heavier.  A 
balloon  rises  in  the  air  because  it  is  filled  with  some  gas 
lighter  than  air,  usually  hydrogen. 

Air  Pressure. — Air  is  like  water  in  that  the  pressure 
increases  with  its  depth.  It  is  denser  at  the  bottom, 
i.  e.,  near  the  earth's  surface,  or,  rather,  at  sea-level. 


Fig.  27. — Diagram  illustrating  increase  of  pressure  with  depth. 

Illustration. — Place  several  pillows  in  a  pile;  note  that  the 
lower  one  is  much  flattened,  each  successive  one  less  so.  This 
illustrates  how  the  weight  of  the  upper  air  compresses  the  lower 
portions  and  drives  the  molecules  closer  together. 

The  air  pressure  at  any  point  equals  the  weight  of 
the  column  of  air  which  is  above  it,  the  height  of  this 
column  being  the  distance  that  the  atmosphere  extends. 


76  PRACTICAL  PHYSICS  FOR  NURSES 

It  can  be  readily  seen  that  this  pressure  is  greater  at 
sea-level  than  at  an  altitude. 

Experiments. — Tie  a  piece  of  thin  rubber  (the  wrist  of  an  old 
rubber  glove  is  suitable)  over  the  mouth  of  a  small  funnel.  Connect 
the  funnel  with  a  piece  of  rubber  tubing.  With  your  mouth  with- 
draw some  of  the  air  in  the  funnel  and  clamp  the  tube.  The  rub- 
ber stretched  over  the  funnel  will  bulge  inward  because  of  the  external 
air  pressure. 

Remove  the  rubber,  leave  the  tubing.  Place  the  funnel  against 
the  cheek,  if  it  is  small  enough  to  fit  snugly;  withdraw  air  by  means 
of  the  tubing.  The  cheek  will  be  pulled  into  the  funnel,  or,  in 
reality,  pushed  in  by  the  air  in  the  tissues  and  the  cavity  of  the 
mouth  pressing  outward.  The  blood  in  the  small  vessels  is  also 
forced  in — shown  by  the  redness  which  appears — because  the 
blood-pressure  from  within  remains  the  same  while  the  air  pressure 
from  without  is  relieved.  This  is  the  principle  of  dry  cupping, 
which  is  used  to  bring  blood  to  the  surface  of  a  small  area.  The 
breast-pump  works  upon  the  same  principle. 


Fig.  28. — Breast-pump  and  cupping-glass. 

The  air  pressure  at  sea-level  is  14.7  pounds  to  the  square 
inch.  Our  bodies,  therefore,  are  constantly  sustaining 
a  weight  of  about  15  tons  of  air.  We  do  not  feel  it  (1) 
because  the  solid  portions  of  the  body  are  very  resist- 
ant, (2)  because  the  body  fluids  are  not  compressible, 


PNEUMATICS  77 

(3)  but  chiefly  because  the  gases  in  the  body  are  of  the 
same  density  as  the  air  and  so  equalize  the  pressure. 

The  feeling  of  pressure  experienced  by  those  who  climb 
high  mountains  is  due  to  the  fact  that  the  air  in  their 
tissues  does  not  escape  nor  become  thin  as  rapidly  as 
that  outside.  The  ear  drum  has  been  known  to  burst 
at  a  high  altitude  on  account  of  the  difference  in  air 
pressure  on  its  two  sides,  especially  if  the  eustachian 
tube  be  partly  blocked- 

Effects  of  Air  Pressure. — Scientists  of  the  old  times 
formulated  a  law,  "Nature  abhors  a  vacuum."  Later 
scientists  explained  this  law  by  the  discovery  of  the  laws 
of  air  pressure.  A  vacuum  is  the  term  used  to  describe 
an  enclosed  space  where  there  is  little  or  no  air.  A  perfect 
vacuum  has  never  been  obtained. 

When  we  begin  to  expel  the  air  from  any  space,  more 
air  tries  to  get  in.  If  a  possible  opening  is  blocked  by 
liquid  or  solid  material,  the  external  air  will,  if  possible, 
push  the  liquid  or  solid  in  ahead  of  itself  in  its  struggle 
to  enter.  In  using  a  medicine-dropper  we  press  the 
air  out  of  the  rubber  bulb  and  dip  the  glass  point  into 
a  liquid;  since  the  air  outside,  pressing  on  all  the  liquid 
in  the  container,  is  kept  away  from  the  entrance  to  the 
tube  by  it,  it  forces  the  fluid  into  the  tube. 

Experiments. — Push  an  empty  tumbler  mouth  downward  into 
water.  Note  that  the  water  rises  only  a  very  little  way  into  the 
glass,  being  kept  out  by  the  air  which  is  there.  Note  the  shape 
of  the  surface  of  the  water  inside  the  glass.  Push  a  large  cork  into 
the  water  and  release  it  under  the  tumbler.  What  occurs,  and  why? 


78  PRACTICAL  PHYSICS  FOR  NURSES 

Fill  a  glass  tube  with  water,  close  the  upper  end  with  the  finger, 
and  dip  the  lower  end  in  water.  The  water  remains  in  the  tube 
because  of  the  pressure  of  the  air  upon  the  surface  of  the  water  in 


Fig.  29. — Tumbler  inverted  in  water,  showing  how  the  air  prevents 
the  water  from  entering.     (Note  shape  of  water  surface.) 

the  vessel.  When  the  finger  is  removed  from  the  top  of  the  tube, 
the  air  pressure  comes  directly  upon  the  water  in  the  tube  and 
causes  it  to  fall. 


Fig.  30. — Upward  pressure  of  the  air  (Butler,  "Household  Physics"). 


Fill  a  small  tumbler  brimful  of  water;  press  a  smooth  piece  of 
paper  on  top;  holding  the  paper  tightly,  turn  the  tumbler  upside 
down;  remove  the  hand  which  holds  the  paper  in  place.  The  paper 


PNEUMATICS 


79 


remains.  The  water  also  remains  in  the  tumbler.  Both  are  held 
in  place  by  the  air  pressure  from  below  upward,  the  glass  prevent- 
ing the  air  pressure  from  above  from  acting  upon  the  water.  (Grav- 
ity is  also  partly  overcome  by  the  adhesion  between  the  wet  paper 
and  the  edge  of  the  tumbler.) 

Vacuum    Fountain    (Fountain    in    Vacua). — Have    a 
quart  flask  fitted  with  a  tight  cork,  through  which  is  a 


Fig.  31. — Fountain  in  vacua. 

small  glass  tube  reaching  halfway  to  the  bottom.  Ex- 
haust as  much  air  as  possible  from  the  flask  by  suction 
upon  the  tube,  put  the  ringer  tightly  over  the  end  of  the 
tube,  dip  the  end  in  water,  and  release  the  finger.  The 


8o 


PRACTICAL  PHYSICS  FOR  NURSES 


water  will  rush  into  the  flask  with  force  enough  to  pro- 
duce a  fountain. 

Hero's  Fountain. — Put  some  water  into  the  flask, 
well  above  the  end  of  the  tube.  Blow  through  the  tube 
until  the  air  inside  is  compressed  as  much  as  possible. 


Fig.  32. — Hero's  fountain. 

Place  the  finger  over  the  end  of  the  tube  to  keep  the  com- 
pressed air  from  escaping.  Release  it  suddenly,  and 
the  confined  air  will  force  water  out  through  the  tube 
like  a  fountain. 

Applications  of  the  Laws  of  Air  Pressure. —  Hypoder- 
mic or  dressing  syringes  to  work  well  must  have  pistons 


PNEUMATICS  8 1 

that  are  air-tight.    When  the  end  of  the  syringe  is 

dipped  in  fluid  and  the  piston  drawn  back  in  an  attempt 

to  create  a  vacuum,  the  pressure  of  the  outside  air 

forces  the  fluid  up  into  the  syringe  and 

so  fills  it.     Any  air  remaining  in  the 

syringe  will  force  the  fluid  out  ahead 

of  it,  so  long  as  the  syringe  is  held  with 

its  needle  pointing  down.    If  we  wish  to 

get  the  air  all  out  of  the  syringe,  we 

must  hold  it  with  the  needle  pointing 

directly  up,  so  that  the  lighter  air  may 

make  its  exit  through  the  needle  before 

the  heavier  fluid.     (In  injecting  under 

the  skin,  we  force  the  liquid,  by  means 

of  the  piston  and  our  fingers,  into  the 

resisting  tissues.) 

The  atomizer  is  dependent  upon  the 
principles  of  air  pressure.     A  stream  of 

air  from  the  bulb  is  forced  over  the  top     Fig>  33-— Hypo- 
dermic      syringe 
of  the  upright  tube  which  dips  into  the   (Morrow). 

reservoir  of  liquid;  this  reduces  the  ex- 
ternal air  pressure  upon  the  contents  of  this  tube.  The 
pressure  upon  the  surface  of  the  body  of  fluid  in  the 
reservoir  pushes  the  fluid  up  this  tube  in  consequence. 
The  jet  of  air  from  the  bulb  at  the  same  time  blows  the 
liquid  away  in  the  form  of  a  fine  spray. 

The  siphon  is  a  tube  bent  into  a  U  shape,  open  at  both 
ends,  one  arm  being  longer  than  the  other.     Fill  the  entire 


§2  PRACTICAL  PHYSICS  FOR  NURSES 

tube  with  water,  and  holding  a  finger  over  the  end  to 
prevent  its  escape,  dip  the  short  arm  into  a  container 
of  water,  dropping  the  longer  arm  outside.  Release  the 


Fig.  34. — Diagram  of  atomizer. 

finger  and  the  water  will  run  out  through  the  siphon  so 
long  as  the  short  arm  dips  into  the  water  in  the  container. 
The  explanation  is  as  follows:  The  pressure  upon  the 
fluid  in  either  arm  is  the  atmosphere  minus  the  weight 


Fig-  35- — The  siphon. 

of  the  water  in  that  arm.  This  makes  the  pressure 
greater  in  the  short  arm  and  less  in  the  long  arm;  the 
fluid  moves  in  the  direction  of  least  resistance. 


PNEUMATICS  83 

The  stomach-tube  is  a  siphon.  The  short  arm  is  in- 
side the  stomach,  the  long  arm  outside.  Water  poured 
into  the  container  (the  stomach)  will  run  out  again 
when  the  long  arm  is  lowered,  providing  the  tube  re- 
mains filled  with  water  while  the  change  in  the  position 
of  the  long  arm  is  being  made.  If  all  the  fluid  in  the 
tube  is  allowed  to  run  into  the  stomach  before  reversing, 
there  will  be  no  siphon  action.1  The  bulb  which  is 
placed  on  some  of  the  stomach-tubes  is  a  variety  of 
pump  (see  Chapter  VI)  which  can  be  used  instead  of  the 
siphon. 

SUMMARY 

In  gases  the  molecules  have  no  cohesion,  but  tend  to 
flee  from  each  other. 

Gases  are  very  elastic  and  very  compressible. 

Whenever  gases  are  brought  into  contact,  they  dif- 
fuse as  liquids  do,  but  more  rapidly.  Upon  this  fact 
depends  our  ability  to  ventilate  rooms  and  buildings. 

Air  is  the  most  important  gas.  It  is  a  mixture  of 
four-fifths  nitrogen,  one-fifth  oxygen,  a  little  carbon 
dioxid,  watery  vapor,  and  other  materials.  It  covers 
the  earth's  surface  7  or  8  miles  deep,  being  more  dense 
at  sea-level  because  of  the  weight  of  the  upper  layers. 
Air  pressure  increases  with  depth. 

The  air  pressure  at  sea-level  is  14.7  pounds  to  the 
square  inch.  We  do  not  feel  it  because  the  solid  por- 

1  It  is  wise  to  have  this  actually  illustrated  in  class,  using  a 
pitcher  or  other  container  in  place  of  the  stomach. 


84  PRACTICAL  PHYSICS  FOR  NURSES 

tions  of  our  bodies  are  very  resistant,  because  the  body 
fluids  are  not  compressible,  and  because  the  body  con- 
tains considerable  air  and  so  equalizes  the  pressure 
outward  and  inward. 

The  breast-pump,  the  hypodermic,  the  dressing  syr- 
inge, cupping-glasses,  the  stomach-tube,  etc.,  are  based 
upon  the  laws  of  air  pressure.  Explain  the  working 
of  each  of  them. 


CHAPTER  VI 
PNEUMATICS  (Continued) 

LAWS  RELATING  TO  GASES 

Pumps  are  machines  for  lifting  and  transferring  fluids 
from  one  place  to  another.  Their  action  depends  upon 
air  pressure.  They  are  of  two  sorts — lifting  and  force- 
pumps. 

The  lifting  pump  has  a  tube  which  dips  into  water 
or  other  fluid,  at  its  lower  end,  where  there  is  placed  a 
valve  that  opens  only  inward.  High  above  this,  at- 
tached to  the  pump  handle,  there  is  a  "sucker,"  a 
tight-fitting  piston  pierced  by  a  valve  that  opens  only 
upward.  When  the  sucker  is  raised  by  means  of  the 
handle  (a  lever),  air  pressure  is  taken  off  the  surface  of 
the  small  body  of  water  in  the  tube;  the  air  pressure 
upon  the  surface  of  the  water  in  the  well  forces  it  up 
the  tube.  (See  Laws  and  Experiments  in  Chapter  V.) 
When  by  the  action  of  the  pump  handle  the  sucker  is 
lowered,  the  weight  of  the  water  in  the  tube  closes  the 
valve  at  its  lower  end  and  prevents  the  contents  from 
running  back  into  the  well.  By  repeating  the  process, 
more  and  more  water  accumulates  in  the  tube  until  it 
is  high  enough  to  run  out  of  the  spout  near  the  top. 

The  force-pump  has  a  one-way  valve  at  the  lower 

85 


86 


PRACTICAL  PHYSICS  FOR  NURSES 


end  of  the  tube  the  same  as  in  the  lifting  pump,  but  its 
piston  is  solid.  The  second  valve  is  at  the  side  of  the 
tube,  and  opens  only  outward,  emptying  into  a  tube 
which  forms  the  spout.  When  the  piston  is  raised,  the 


Fig.  36. — Lifting  pump  (Butler,  "Household  Physics"). 

main  tube  partly  fills  with  water,  exactly  as  in  the  lift- 
ing pump;  when  it  is  lowered,  the  weight  of  the  water 
closes  the  valve  at  the  bottom.  The  movement  being 


PNEUMATICS  87 

repeated,  continued  pressure  forces  the  side  valve  open 
and  the  water  up  the  side  tube  and  out  at  the  spout. 

A  Davidson  (or  bulb)  syringe  is  a  variety  of  force- 
pump,  at  least  so  far  as  the  action  of  the  valves  is  con- 
cerned. Pressing  the  bulb  while  the  end  of  the  tube 
dips  into  water  tends  to  create  a  vacuum,  and  when  the 
pressure  is  released,  water  runs  up  into  the  tube  and 


Fig-  37- — Force-pump  (Butler,  "Household  Physics"). 

bulb.  A  second  pressure  forces  the  water  in  the  tube 
against  the  valve  at  its  lower  end  and  closes  it,  at  the 
same  time  pushing  it  against  the  outward-opening 
valve  of  the  rectal  or  delivery  tube  and  forcing  the  wa- 
ter out  through  it. 

The  bulb  of  a  stomach-tube  works  exactly  as  does  that 
of  a  Davidson  syringe. 


88  PRACTICAL  PHYSICS  FOR  NURSES 

The  heart  is  a  force-pump.  The  hollow  organ  re- 
sembles the  bulb  of  a  syringe,  except  that  the  force 
which  contracts  it  is  furnished  by  the  heart  muscle 
itself,  situated  in  the  wall.  There  is  no  piston,  but  the 
expansion  and  relaxation  makes  the  cavity  alternately 
larger  and  smaller.  When  the  auricles  contract,  the  one- 
way valves  (the  bicuspid  and  tricuspid)  are  forced  open 
and  the  blood  runs  into  the  ventricles.  When  the 


Fig.  38. — Dilation  and  contraction  of  ventricles  of  the  heart. 

ventricles  contract,  these  valves  are  forced  shut  by  the 
weight  of  the  blood  against  them,  and  the  semilunar 
valves  are  pushed  open;  the  blood  is  thus  forced  out  into 
the  vessels,  from  the  right  ventricle  to  the  lungs  for 
purification,  and  from  the  left  ventricle  into  the  aorta, 
and  so  through  the  body.  The  impulse  of  the  heart- 
beat as  it  forces  the  blood  out  through  the  arteries  is 
transmitted  to  the  very  ends  of  the  vessels  and  starts 
the  blood  on  its  way  through  the  capillaries. 
In  the  return  venous  circulation  the  flow  is  largely 


PNEUMATICS  8<J 

due  to  the  pressure  of  fluid  back  of  it  and  to  muscular 
action.  In  the  large  veins  of  the  lower  limbs,  however, 
this  pressure  is  not  enough  to  overcome  the  action  of 
gravity.  One-way  valves  are,  therefore,  introduced, 
which  hold  the  blood  in  place  until  additional  force 
from  behind  pushes  them  open  and  makes  the  blood  rise. 
The  action  is  much  like  that  of  the  lifting  pump. 

The  sphygmograph,  or  sphygmomanometer,  is  a  machine  which  re- 
cords the  force  of  the  heart-beat.  A  button  is  fastened  over  some 
artery  that  comes  conveniently  near  the  surface,  and  a  series  of  levers 
transmit  the  impulse  against  it  to  a  fine  needle  which  traces  the 
record  of  its  rise  and  fall  upon  a  specially  prepared  paper.  Any 
irregularities  or  lack  of  force  are  noted  by  this  tracing. 


Fig-  39- — Valves  in  vein. 

Steam  Apparatus. — Steam  is  a  gas.  It  occupies  about 
1700  times  as  much  space  as  the  water  from  which  it 
is  made.  When  confined  within  a  boiler  or  other  con- 
tainer and  kept  hot  (*'.  e.,  in  a  gaseous  state)  it  struggles 
to  escape.  This  attempt  to  escape  is  used  to  produce 
motion,  work  of  various  sorts.  (In  many  steam  appli- 
ances the  heat  is  an  important  factor.  See  Chapter 
VII.)  In  the  steam  engine  the  steam,  in  its  effort  to 
escape,  drives  before  it  with  considerable  force  the 
piston,  a  solid  body.  The  piston  is  attached  to  a  wheel 
by  one  or  more  levers,  and  the  wheel  moves  with  the 
movement  of  the  piston.  The  motion  thus  gained  is 


QO  PRACTICAL  PHYSICS  FOR  NURSES 

transferred  by  one  mechanism  or  another  to  whatever 
machinery  it  is  desired  to  drive. 

Respiration. — The  act  of  breathing  involves  the  laws  of 
pneumatics.  When  the  chest  wall  is  pulled  outward  by 
the  action  of  the  chest  muscles,  and  the  diaphragm  is 
lowered,  the  external  air  rushes  in  to  fill  what  would 
otherwise  be  a  vacuum.  When  the  chest  muscles  relax 
and  let  the  chest  wall  fall  inward  and  the  diaphragm 


Fig.  40. — Diagram  of  air-cell  of  lung. 

rise,  making  the  space  smaller,  the  air  in  the  chest  is 
forced  out.  This  alternate  intake  and  expulsion  of 
air  we  call  inspiration  and  expiration.  About  30  cubic 
inches  of  air  enter  and  are  expelled  with  each  respiration. 
The  muscular  action  takes  air  into  the  lungs  as  far 
as  the  smaller  bronchi.  Then  the  law  of  diffusion  of 
gases  comes  into  action,  and  an  interchange  takes  place 
between  the  incoming  oxygen  and  the  carbon  dioxid  in 


PNEUMATICS  91 

the  blood-stream  in  the  lungs.  This  carbon  dioxid, 
one  of  the  important  waste  materials  of  the  body,  is 
a  gas  carried  by  the  venous  blood  into  all  the  capillaries 
of  the  lungs.  The  very  thin  membrane  between  the 
capillaries  and  the  air  cells  of  the  lungs  permits  it  to 
escape,  by  osmosis,  into  the  air  cells,  and  at  the  same 
time  allows  the  oxygen  which  has  come  in  to  pass,  by 
the  same  force,  into  the  blood-stream.  (Note  that  air 
is  a  mixture,  not  a  compound;  its  oxygen  is,  therefore, 
free  and  ready  to  exchange  places  with  the  carbon 
dioxid.)  The  membrane  lining  the  air-cells  is  just 
strong  enough  to  prevent  the  fluid  blood  from  passing. 
If  it  is  weakened  by  disease,  we  have  hemorrhage  from 
the  lungs. 

VENTILATION 

Principles  of  Ventilation. — If  we  open  a  window  on  a 
warm,  perfectly  still  day,  we  presently  feel  the  outside 
air  coming  in.  This  is  due  to  the  law  of  diffusion  of 
gases.  A  certain  amount  of  such  exchange  of  outdoor 
and  indoor  air  also  takes  place  constantly  through  the 
cracks  in  our  dwellings  and  even  through  the  walls 
themselves,  which  are  more  or  less  porous.  The  phe- 
nomenon is  more  evident  when  a  larger  opening,  like  a 
window  or  door,  is  provided. 

Diffusion  of  gases  takes  place  more  rapidly  when  there 
is  wind  to  drive  the  molecules  forward.  It  is  also  in- 
creased by  marked  difference  in  temperature. 

Heat  pushes  the  molecules  of  air  farther  apart,  so 


92  PRACTICAL  PHYSICS  FOR  NURSES 

that  warm  air  always  struggles  more  vigorously  to  get 
away  than  does  cold  air.  Upon  opening  the  window  in 
very  cold  weather,  you  can  feel  the  warm  air  going  out 
for  some  time  before  the  cold  air  appears  to  come  in. 

Warm  air,  because  its  molecules  are  farther  apart, 
is  lighter  than  cold  air.  In  a  closed  room  warm  air  rises, 
partly  because  of  its  lighter  weight  and  partly  because 
of  the  pressure  of  the  cooler  air  which  remains  at  the 
bottom.  Hang  two  thermometers  in  a  closed  room, 
one  near  the  floor  and  one  near  the  ceiling.  There  will 
be  a  number  of  degrees  variation  in  their  readings,  es- 
pecially in  a  room  which  is  artifically  heated. 


Fig.  41. — How  the  draft  in  a  chimney  is  produced. 

The  Draft  in  a  Chimney. — Warm  air,  produced  by  a 
fire,  rises  because  the  cold  air,  which  is  heavier,  pushes 
it  up  from  the  bottom.  We  say  that  a  chimney  draws, 


PNEUMATICS  93 

but  the  word  is  incorrect,  since  the  draft  is  due  to  the 
push  of  the  cold  air  from  the  room  below,  not  to  any 
pull  of  warm  air  from  above.  The  effect  is  the  same,  but 
our  mode  of  expression  creates  confusion  in  our  minds. 

Experiment. — Prepare  an  air-tight  box  with  two  holes  in  the 
lid;  over  each  hole  set  a  lamp-chimney  and  make  the  joint  air- 
tight. Lower  a  bit  of  lighted  candle  into  one  of  the  chimneys; 
the  air  thus  heated  rises,  and  fresh,  cool  air  passes  down  through 
the  other  chimney  to  take  its  place.  Show  the  draft  thus  produced 
by  burning  touch  paper  or  something  which  smokes  freely  over  the 
cool  chimney.  This  method  of  introducing  fresh  air  into  a  room 
is  called  gravity  ventilation. 

The  above  simple  principles  are  the  basis  of  our  heat- 
ing and  ventilating  systems,  no  matter  how  compli- 
cated they  may  seem. 

To  heat  a  room  economically,  the  warmth  should  come 
from  near  the  floor,  because  warm  air  always  rises. 

To  "ventilate  a  room  we  must  have  somewhere  openings 
of  sufficient  size  to  permit  diffusion  of  gases  to  take  place 
as  rapidly  as  is  required  by  the  number  of  occupants; 
1000  cubic  feet  of  air  space  for  each  person  (a  space  10 
feet  square  by  10  feet  high)  is  estimated  to  be  the  mini- 
mum requirement  in  a  closed  room.  Ventilation  must  be 
rapid  and  thorough  to  keep  this  air  properly  oxygenated. 
If  the  openings  provided  for  the  entrance  of  warmed  air 
and  the  escape  of  impure  air  are  not  properly  located, 
diffusion  will  not  be  satisfactorily  accomplished.  Figure 
42  shows  the  possibilities  in  such  cases. 

In  the  so-called  "natural"  ventilation — i.  e.,  by  open- 


94 


PRACTICAL  PHYSICS  FOR  NURSES 


ing  the  windows — one  should  open  them  at  both  top 
and  bottom,  so  as  to  provide  for  proper  circulation  of  air. 


1 

INLET 

'  —  ^          —  ^         --^ 

1 

-----  »»'-L-/---- 

OVTL6T 

^~~"             v^^^^^X^X^ 

Fig.  42. — Air  circulation  in  forced  ventilation  systems. 

Ventilating  Systems. — "Natural"  ventilation  is  un- 


PNEUMATICS  95 

satisfactory  in  very  hot  or  very  cold  weather;  in  very 
warm  weather  the  diffusion  of  air  takes  place  too  slowly; 
in  cold  weather,  too  rapidly. 

Artificial  ventilation  is  a  combination  of  heating  with 
ventilation.  Some  systems  embody  the  theory  that 
fresh  warmed  air  goes  to  the  ceiling,  while  foul  air  drops 
to  the  floor;  but  authorities  do  not  agree  in  this  matter. 


Fig.  43. — Natural  ventilation  (Butler,  "Household  Physics"). 

The  correct  and  efficient  method  is  to  arrange  the  loca- 
tion of  inlets  and  outlets  so  that  the  air  in  every  room 
must  be  thoroughly  stirred  by  the  draft  from  the  heating 
system;  just  what  these  locations  are  is  still  under  dis- 
cussion. 

There  are  two  sorts  of  heating-ventilating  systems  in 
use.  One  is  the  vacuum,  in  which  the  air  is  drawn  out 
of  the  rooms  by  suction.  The  other  is  the  plenum,  in 


96  PRACTICAL  PHYSICS  FOR  NURSES 

which  air  is  forced  into  the  room,  usually  by  means  of  a 
fan  driven  by  a  motor.  Neither  system  works  well  in 
combination  with  open  windows. 

An  objection  to  all  forced  ventilating  systems  is  that 
they  stir  up  dust  and  bacteria.  This  is  overcome  in 
some  cases  by  using  a  "washed  air"  system,  in  which 
dust  and  bacteria  are  removed  from  the  air  before  it 
enters  the  room.  This  is  only  partially  successful, 
because  it  does  not  take  care  of  the  dust  and  bacteria 
which  originate  in  the  room. 

SUMMARY 

Pumps  are  machines  for  transferring  fluids  from  one 
place,  or  one  level,  to  another. 

Lifting  and  force-pumps  are  similar  in  their  action. 
Each  has  a  piston  working  in  a  tube  which  dips  into  the 
water  or  other  fluid.  Each  has  a  one-way  valve  at  the 
lower  end  of  the  tube,  which  permits  the  fluid  to  enter, 
but  not  to  return.  The  lifting  pump  has  a  valve  in 
the  piston;  the  force-pump,  one  at  the  side  of  the  tube. 
In  each  form  of  machine  the  repeated  action  of  the  pump- 
handle  transferred  to  the  piston  lifts  a  portion  of  the 
liquid  into  the  tube,  until  a  sufficient  quantity  accumu- 
lates to  run  or  be  forced  out  of  the  spout. 

The  bulb  syringe  and  the  bulb  of  the  stomach-tube 
are  force-pumps. 

The  action  of  the  human  heart  is  like  that  of  a  force- 
pump,  the  power  being  the  muscle  in  its  wall. 


PNEUMATICS  97 

In  the  steam  engine  the  piston  is  driven  by  the  force 
of  steam  trying  to  escape  its  bounds.  The  motion  thus 
produced  is  transferred  by  an  appropriate  mechanism 
to  any  desired  machine. 

Respiration  is  carried  on  in  accordance  with  the  laws 
of  pneumatics.  The  actual  exchange  of  oxygen  and 
carbon  dioxid  is  due  to  osmosis. 

The  ventilation  of  rooms  and  buildings  involves  the 
law  of  diffusion  of  gases,  and  the  law  that  heated  gases 
rise  and  cold  ones  fall. 

Natural  ventilation  is  satisfactory  only  in  moderate 
weather.  Artificial  heating  and  ventilating  systems 
work  better  in  very  cold  weather;  they  are  of  two  prin- 
cipal sorts,  one  in  which  the  air  is  drawn  out  of  the  rooms 
by  suction,  the  other  in  which  it  is  forced  in  by  a  fan. 
All  artificial  ventilation  stirs  up  dust  and,  therefore, 
bacteria. 

Authorities  disagree  in  regard  to  both  theories  and 
methods  of  ventilation. 


CHAPTER  VII 

HEAT 

Heat  is  motion.  We  have  learned  that  the  molecules 
of  all  substances,  however  dense,  are  separated  from 
each  other,  no  one  touching  another.  We  have  now  to 
learn  that  these  molecules  are  always  in  motion.  (The 
motion  is  probably  vibratory.)  This  molecular  motion 
is  heat. 

Intensity  of  Heat. — A  substance  whose  molecules  are 
moving  very  slowly  is  cold.  One  in  which  they  are 
moving  more  rapidly  is  warm.  One  in  which  they 
move  with  great  rapidity  is  hot.  When  we  heat  an  ob- 
ject, we  stimulate  its  molecules  to  more  rapid  motion. 
When  we  cool  it,  we  quiet  their  movements. 

Heat  may  be  transferred  from  one  body  to  another 
just  as  motion  or  other  sorts  of  energy  may,  by  obedience 
to  the  laws  that  govern  the  transfer. 

Sources  of  Heat. — Directly  or  indirectly  nearly  all  of 
our  heat  comes  from  the  sun.  Coal  is  indirectly  the 
energy  of  the  sun  stored  up  ages  ago;  petroleum  likewise. 

Heat  may  be  produced  by  (1)  friction;  (2)  percussion; 
(3)  chemical  action,  and  (4)  electric  action. 

Experiment. — Rub  a  smooth  metal  button  rapidly  back  and 
forth  on  a  rough  woolen  cloth.     The  button  becomes  quite  warm, 
an  example  of  heat  produced  by  friction. 
98 


HEAT  99 

Friction  is  arrested  motion,  i.  e.,  motion  converted  into 
heat,  merely  a  different  manifestation  of  the  same  force. 

Because  of  this,  we  must  often  take  means  to  get 
rid  of  friction  when  it  is  producing  heat  which  we 
do  not  want  (see  page  56).  For  example,  unless  the 
bearings  of  wheels  are  kept  oiled — the  two  portions  of 
metal  separated  by  means  of  the  oil — the  friction  caused 
by  their  rapid  movement  makes  them  become  hot  and 
may  even  cause  fire.  A  "hot  box"  on  a  railway  car  is 
the  result  of  friction. 

Experiment. — Strike  a  coin  or  other  bit  of  metal  hard  and 
rapidly  with  a  hammer.  Both  hammer  and  coin  become  warm, 
the  heat  being  produced  by  percussion.  Here  again  we  have  heat 
as  the  result  of  arrested  motion. 

Add  sulphuric  acid  to  a  small  quantity  of  cold  water.  Test 
with  a  thermometer.  The  liquid  and  the  container  become  hot, 
an  example  of  heat  produced  by  chemical  action. 

The  incandescent  electric  light,  the  electric  flat-iron, 
and  the  electric  cooker  are  examples  of  heat  produced 
by  electric  action.  (See  Chapter  XI.) 

Bodily  heat  is  produced  by  muscular  action,  by  the 
chemical  changes  which  take  place  in  the  process  of  nutri- 
tion, by  the  circulation,  etc.  Bodily  heat  is  lost  by  con- 
duction, radiation,  and  evaporation  (see  pages  107,  115, 
and  125).  The  heat  loss  and  production  are  regulated 
by  certain  centers  in  the  brain.  Normal  temperature  is 
the  result  of  a  perfect  balance  between  the  heat-produc- 
ing and  the  heat-losing  processes.  Fever  is  the  result 
of  either  overproduction  or  poor  elimination  of  heat, 


100  PRACTICAL  PHYSICS  FOR  NURSES 

usually  the  latter.  Subnormal  temperature  is  usually 
due  to  lack  of  heat  production,  very  occasionally  to  ex- 
cessive loss  of  heat. 

Burning  is  a  chemical  process,  in  which  the  oxygen  of 
the  air  combines  actively  with  the  material  of  the  fuel, 
changing  it  into  an  entirely  different  substance.  The 
products  are  smoke,  gases,  and  ashes,  with  the  inci- 
dental products  of  heat  and  light. 


Fig.  44. — Drafts  in  a  kitchen  stove  (Butler,  "Household  Physics"). 

If  we  wish  a  fire  to  burn  well  we  must  provide  for 
the  admission  to  it  of  plenty  of  oxygen;  we  do  this  by 
openings  in  our  stoves  and  heaters  which  we  call  drafts 
or  dampers.  Closing  a  stove  draft  shuts  off  the  supply 
of  oxygen,  therefore  checks  the  process  of  combustion. 

In  a  kitchen  stove  there  are  usually  four  drafts  or 
dampers  which  regulate  the  activity  of  the  fire  and 


HEAT  101 

determine  the  direction  in  which  the  heat  is  to  be  thrown. 
When  the  under  damper  at  the  fire-box  is  open  there 
is  a  draft  of  air  through  the  fire,  making  it  burn  better. 
If  this  is  closed  and  the  upper  one  is  opened  the  draft 
passes  over  the  fire  and  it  burns  more  slowly.  The 
damper  in  the  smoke  pipe  is  an  additional  check  upon 
the  draft,  slowing  the  fire  still  more.  The  oven  damper 
directs  the  hot  gases  around  the  oven  instead  of  over  it. 

Temperature  is  the  degree  of  heat  in  an  object  or  sub- 
stance. It  is  not  the  amount  of  heat,  or  large  bodies 
would  always  be  hotter  than  small  ones. 

We  use  the  term  "warm"  for  things  which  are  of  a 
temperature  about  that  of  the  human  body  (98|°  F.). 
We  say  things  are  hot  or  cold  when  they  are  considerably 
above  or  below  that  temperature.  Our  statements  in 
this  respect  are  only  relative,  since  we  call  tea  cold  when 
it  has  a  temperature  of  105°  F.,  while  a  bath  at  105°  F. 
is  considered  hot. 

Our  own  sensations  are  not  sufficiently  accurate  to 
enable  us  to  judge  heat  by  them,  as  they  are  dependent 
upon  so  many  factors.  A  blindfolded  person  cannot 
be  sure  whether  a  substance  is  very  cold  or  very  hot, 
since  the  sensation  is  almost  exactly  the  same  in  each 
case. 

Experiment. — Have  three  containers,  one  of  hot  water,  one  of 
cold,  and  one  of  lukewarm.  Put  the  fingers  of  one  hand  into 
the  cold  water  while  those  of  the  other  hand  are  in  the  hot.  After 
a  moment  put  both  hands  into  the  lukewarm  water.  It  will  feel 
cool  to  the  hand  from  the  hot  water  and  warm  to  the  hand  from  the 
cool  water. 


102  PRACTICAL  PHYSICS  FOR  NURSES 

Effect  of  Heat. — Heat  produces  the  following  effects: 

1.  Rise  in  temperature. 

2.  Increase  in  volume   (the  molecules  being  driven 
farther  apart,  the  substance  requires  more  room.) 

3.  Increase  of  pressure  upon  the  container.     This  is 
due  to  the  increased  volume. 

4.  Change  in  physical  state,  as  melting,  vaporization, 
etc. 

5.  Change  in  character,  as  in  burning  or  other  chem- 
ical process. 

Expansion  and  Contraction. — Since  heat  is  motion, 
and  increased  motion  tends  to  drive  the  molecules  of  a 
substance  farther  apart,  it  is  easy  to  understand  that 
heat  increases  the  volume  of  a  substance,  i.  e.,  expands 
it.  Absence  or  lessening  of  heat  causes  the  opposite 
effect,  contraction.  We  have,  therefore,  the  law,  Heat 
expands  and  cold  contracts.1 

Experiment. — Use  the  flask  with  a  bent  tube  through  the  cork. 
Place  the  end  of  this  tube  in  water.  Heat  the  empty  flask.  Bubbles 
of  air  will  be  seen  pushing  their  way  through  the  water  because  the 
heat  expands  the  air  in  the  flask.  Without  removing  the  end  of 
the  tube  from  the  water,  cool  the  flask  by  pouring  cold  water  over 
it.  Water  will  be  forced  up  into  the  tube  on  account  of  the  les- 
sened air  pressure  in  the  flask. 

Uneven  expansion  or  contraction  may  encounter  re- 
sistance at  some  point  and  a  crack  or  breakage  result, 
if  the  material  is  brittle.  This  is  observed  in  glassware, 

1  We  are  familiar  with  the  fact  that  gloves  and  shoes  fit  more 
snugly  when  the  hands  and  feet  are  very  warm.  This  is  almost 
entirely  due  to  the  above  law. 


HEAT  103 

which  is  almost  sure  to  crack  if  either  heat  or  cold  is 
suddenly  applied  to  one  portion;  this  portion  expands 
or  contracts,  as  the  case  may  be,  while  the  rest  of  the 
utensil  remains  unaffected.  It  is  this  uneven  expansion 
or  contraction  which  causes  the  breakage. 

Water  is  the  one  great  exception  to  the  rule  of  con- 
traction upon  cooling.  It  acts  like  ordinary  materials 
and  contracts  while  cooling  until  a  temperature  of  4°  C. 
is  reached,  when  it  begins  to  expand.  Ice  occupies 
more  space  than  did  the  water  from  which  it  was  made. 
To  this  fact  is  due  the  bursting  of  water-pipes  when 
frozen. 

Measurement  of  Heat. — In  order  to  accurately 
measure  heat  the  thermometer  has  been  devised.  Its 
bulb  contains  some  fluid  which  is  especially  sensitive 
to  heat  and  readily  expands  when  warmed.  The  tube 
provides  an  outlet  for  the  expanding  fluid.  The  scale 
records  the  amount  of  expansion  or  contraction. 

Mercury  is  used  in  thermometers  because  it  is  sensi- 
tive to  heat,  easy  to  see,  etc.  Colored  alcohol  is  also 
used,  especially  in  thermometers  for  use  in  very  cold 
regions  where  mercury  would  freeze.  (Mercury  freezes 
at  40°  F.  below  zero.) 

If  a  thermometer  bulb  is  placed  in  contact  with  any- 
thing hotter  than  is  provided  for  by  the  length  of  its 
tube,  the  force  of  the  expansion  of  the  mercury  will 
burst  the  tube.  (We  all  know  the  unfortunate  pro- 
bationer who  washes  a  thermometer  in  hot  water.) 


104  PRACTICAL  PHYSICS  FOR  NURSES 

If  a  thermometer  bulb  is  placed  in  contact  with  any- 
thing colder  than  the  tube  provides  for,  the  mercury  goes 
into  the  bulb  and  we  cannot  register  it. 

The  clinical  thermometer  is  provided  with  a  contrac- 
tion in  the  tube  at  a  point  below  the  scale.  This  inter- 
feres with  the  free  return  of  the  mercury  when  cooling 
takes  place,  and  so  keeps  in  place  what  has  run  up  the 
tube  until  it  is  shaken  down,  i.  e.,  urged  back  into  the 
bulb  or  toward  it. 

A  thermometer  must  be  very  accurately  made, 
scaled,  and  tested  to  be  of  value. 

There  are  two  sorts  of  thermometers  in  use,  those 
having  the  Fahrenheit  and  those  the  Centigrade  scale.1 
In  the  Fahrenheit  scale,  32°  is  the  freezing-point  of 
water  and  212°  its  boiling-point.  In  the  Centigrade 
scale  (Centigrade  means  "one  hundred  steps")  zero  is 
the  freezing-point  of  water  and  100°  its  boiling-point. 

A  calorie  is  the  standard  of  measurement  for  chemical 
heat.  It  is  the  amount  of  heat  required  to  raise  the 
temperature  of  1  pound  of  water  4  degrees  Centigrade. 

Boiling. — Liquids  are  said  to  boil  when  their  tem- 
perature is  raised  to  the  point  where  they  begin  to  change 
into  vapor.  When  water  is  heated  to  100°  C.  bubbles 
of  steam  are  formed,  which,  being  lighter  than  the 
water,  push  their  way  to  the  surface  and  discharge  into 
the  air.  This  gives  the  appearance  which  we  call 
boiling. 

1  The  Reaumur  scale  is  not  much  used. 


HEAT  105 

The  temperature  of  water  to  which  heat  is  being  ap- 
plied rises  gradually  until  full  boiling-point  is  reached, 
when  it  remains  stationary,  After  a  liquid  is  once 
boiling,  it  cannot  be  made  any  hotter,  though  heat  is  still 
going  into  it.  (See  Latent  Heat,  page  127.)  Test  with  a 
thermometer,  and  see  if  there  is  a  difference  in  tempera- 
ture between  water  that  is  boiling  gently  and  that  boil- 
ing vigorously. 

Variation  in  Boiling-point. — All  liquids  do  not  boil  at 
the  same  temperature.  Alcohol  boils  at  78°  C.,  and 
ether  at  37°  C.  Mercury  (a  liquid  metal)  requires  a 
temperature  of  357°  C.  to  make  it  boil. 

Raising  the  Boiling-point  of  Water. — When  a  liquid 
has  a  solid  substance  dissolved  in  it  the  boiling-point  be- 
comes higher.  A  familiar  example  is  found  in  the  fact 
that  vegetables  cook  more  rapidly  in  salted  water, 
because  its  boiling-point  is  higher  and  more  heat  is 
being  used. 

Experiment. — Put  water  into  two  containers  of  the  same  size. 
Dissolve  2  or  3  teaspoonfuls  of  salt  in  one  of  them.  Heat  both 
until  they  boil.  Test  the  temperature  of  each  with  a  thermometer 
that  has  a  scale  above  212°  F.  The  salted  water  will  be  found 
several  degrees  hotter  than  the  unsalted. 

Air  Pressure  and  Boiling. — The  boiling-point  of  a 
liquid  is  changed  when  the  air  pressure  upon  it  is  changed. 
The  boiling-point  of  water  is  212°  F.  at  sea-level.  As 
one  goes  to  a  higher  altitude  it  becomes  less,  the  difference 
being  1  degree  Fahrenheit  for  every  500  feet  of  alti- 


106  PRACTICAL  PHYSICS  FOR  NURSES 

tude.  In  Denver,  1  mile  above  sea-level,  water  boils 
ar  202°  F.;  on  the  top  of  Pike's  Peak  (14,000  feet)  it 
boils  at  184°  F.;  at  the  latter  place  it  is  impossible  to 
cook  eggs  hard,  because  there  is  not  enough  heat  in 
boiling  water  to  coagulate  the  albumen.  Even  at  1 
mile  above  sea-level  it  takes  appreciably  longer  to  cook 
vegetables,  etc.,  because  boiling  water  is  not  as  hot  as 
at  sea-level. 

Experiment. — Put  some  water  into  a  flask  and  heat  it  to  the 
boiling-point.  Remove  from  the  fire  and  at  once  cork  tightly. 
Turn  the  flask  upside  down  and  pour  cold  water  over  it.  The  cold 
condenses  the  steam  which  is  in  the  flask  and  thus  removes  its  pres- 
sure from  the  surface  of  the  water.  The  water  begins  to  boil  again 
from  the  release  of  pressure.  When  it  again  stops  boiling,  test 
the  temperature.  It  will  be  found  considerably  less  than  212°  F. 

This  phenomenon  is  utilized  in  a  practical  way  in  the 
vacuum  kettle.  Condensed  milk,  for  example,  is  made 
by  evaporating  the  moisture  from  milk  at  a  temperature 
below  212°  F.,  i.  e.,  boiling  it  in  a  kettle  from  which  a 
portion  of  the  air  has  been  pumped,  so  that  the  pressure 
on  the  surface  of  the  liquid  is  much  less  and  the  boiling- 
point  considerably  lowered. 

Steam  Pressure  Apparatus. — Conversely,  if  we  in- 
crease the  pressure  upon  the  surface  of  a  liquid,  we  raise 
its  boiling-point.  "Pressure  cookers"  and  sterilizing 
apparatus  take  advantage  of  the  fact  that  steam  under 
pressure  is  hotter  than  that  which  is  in  contact  with 
the  air.  Cookers  of  this  sort  are  made  steam  tight  and 
strong  enough  to  resist  several  pounds'  pressure.  They 


HEAT  107 

cook  their  contents  at  a  temperature  higher  than  212°  F., 
therefore  more  rapidly  and  thoroughly.  (They  also 
keep  in  the  flavors  which  would  otherwise  escape  with 
the  steam.1) 

In  a  dressing  sterilizer  15  or  more  pounds  of  pressure 
are  used  to  raise  the  steam  to  a  temperature  of  240°  F. 
or  more.  We  call  this  "superheated"  steam,  and  find 
that  it  remains  dry,  that  is,  uncondensed.  This  makes 
the  sterilizing  process  more  sure  because  of  the  higher 
temperature  to  which  possible  germs  are  subjected. 
The  pressure  also  serves  to  force  the  steam  in  among 
the  dressings,  so  that  it  may  reach  every  portion  of  the 
materials  to  be  sterilized.  The  dryness  of  the  steam  is 
an  additional  advantage.  Such  sterilizers  must,  of 
course,  be  fitted  with  safety-valves,  so  that  the  pressure 
may  not  run  so  high  as  to  endanger  the  apparatus. 

(Water  sterilizers  ordinarily  are  devices  for  boiling 
water  under  normal  air  pressure,  and  afterward  either 
keeping  it  hot  or  cooling  it.  They  may  be  arranged  to 
sterilize  under  pressure  at  a  higher  temperature.  Uten- 
sil and  instrument  sterilizers  are  merely  pans  in  which 
the  boiling  is  accomplished  by  gas,  steam,  or  electric 
heat.) 

Evaporation  is  the  process  of  changing  a  liquid  into  a 
gas.  When  a  liquid,  especially  if  warm,  is  left  exposed 
to  the  air  the  molecules  on  its  surface  are  constantly 

1  The  action  of  heat  in  cooking  food  is  largely  due  to  the  chem- 
ical changes  which  it  produces. 


Io8  PRACTICAL  PHYSICS  FOR  NURSES 

leaving  and  going  into  the  air.  With  time,  all  the 
liquid  goes  into  the  air  in  this  way  and  disappears.  It 
has  become  vapor — evaporated.  The  process  is,  as  we 
know,  hastened  by  heat,  and  by  a  draft  of  air  or  wind, 
which  enable  the  molecules  to  detach  themselves  more 
easily;  the  current  also  carries  them  away,  making  room 
for  more  to  rise.  Evaporation  also  takes  place  more 
rapidly  from  a  large  surface,  since  there  are  a  greater 
number  of  molecules  exposed  to  the  air  and  ready  to 
take  flight. 

Applications  of  these  principles  are  familiar.  We 
heat  a  liquid  when  we  wish  it  to  evaporate  quickly. 
We  hang  wet  clothing  in  a  breeze  to  dry  it:  We  spread 
out  damp  materials  when  we  wish  them  to  dry.  We 
use  a  large  open  pan  when  we  wish  its  contents  to  evapo- 
rate or  dry  out,  and  a  smaller  one  with  a  tight  cover  when 
we  wish  to  keep  materials  moist. 

Evaporation  Cools. — Experiments. — Pour  a  little  alcohol  or 
ether  upon  the  hand.  It  feels  cool,  i.  e.,  it  cools  the  hand  as  it 
evaporates.  Hang  two  thermometers  side  by  side.  Cover  the 
bulb  of  one  with  a  bit  of  gauze,  the  end  of  which  dips  into  water. 
Fan  them  vigorously.  The  wet-bulb  thermometer  shows  a  con- 
siderably lower  temperature  than  the  other.1 

The  evaporation  of  perspiration  from  the  surface  of 
the  body  cools  it.  Fanning  cools  a  person  who  is  per- 
spiring by  hastening  evaporation.  Since  there  is  a 
constant  "insensible"  perspiration  going  on  even  in 
cool  weather  (the  amount  is  20  to  30  ounces  in  twenty- 

1  The  Mexican  olio,  a  porous  water-jar,  hung  in  a  draft,  keeps 
water  cool  in  hot  weather  by  evaporation. 


HEAT  109 

four  hours),  its  evaporation  produces  a  considerable 
cooling  of  the  body.  Profuse  perspiration  causes  a 
very  marked  cooling.  On  a  damp  day  the  evaporation 
of  perspiration  takes  place  slowly,  and  we  do  not  get  the 
cooling  action  to  any  extent;  we  therefore  "feel  the  heat." 

The  fan  bath  which  is  given  to  reduce  temperature 
constitutes  a  method  of  causing  moisture  to  evaporate 
rapidly  from  the  surface  of  the  body,  thus  extracting 
heat  from  the  patient.  For  a  similar  reason  a  tepid 
bath  often  reduces  temperature  as  well  as  a  cold  one. 

A  cold  compress  should  always  be  thin,  so  that  evapo- 
ration may  prolong  and  add  to  the  cooling  process,  and 
obviate  frequent  changing.  (Conversely,  a  hot  com- 
press should  always  be  thick  and  covered  well,  in  order 
to  prevent  both  evaporation  and  radiation  of  heat.) 

Condensation  is  the  opposite  of  evaporation,  and  is 
produced  in  an  opposite  way.  If  a  warm  vapor  is  cooled, 
it  condenses,  i.  e.,  becomes  a  liquid  again.  This  is  the 
cause  of  rain;  the  heat  of  the  sun  vaporizes  water  from 
the  sea,  lakes,  etc.,  and  it  is  stored,  still  warm,  in  the 
form  of  clouds.  When  these  clouds  are  struck  by  a 
cold  wind  or  come  into  a  cooler  layer  of  air,  the  vapor 
of  which  they  are  composed  condenses  into  drops  and 
we  have  rain. 

(Snow  is  frozen — crystallized — water  vapor.  Dew  is  caused 
by  the  moisture  in  the  air  condensing  upon  a  surface  which  is 
colder  than  the  air.  The  earth,  grass,  plants,  etc.,  radiate  their 
heat  readily,  therefore  soon  become  cooler  than  the  air.  Frost  is 
frozen — crystallized — dew.) 


no  PRACTICAL  PHYSICS  FOR  NURSES 

Distillation  is  the  process  whereby  a  liquid  is  vaporized 
by  heat  and  the  vapor  collected  and  cooled,  making 
it  into  a  liquid  again.  It  is  commonly  done  by  boiling 
the  liquid  in  a  closed  vessel,  letting  the  vapor  escape 
through  a  long  tube  which  runs  through  cold  water; 
the  large  surface  presented  to  the  cooling  process  makes 
the  vapor  condense  rapidly;  it  drips  from  the  end  of 
the  tube  into  a  container. 


Fig.  45. — Water  still :  A  and  B,  Inlet  and  outlet  for  water  to  cool 
it;  C,  boiler  for  water;  D,  inlet  for  heating  gas;  E,  condenser;  G, 
collecting  pipe  for  steam ;  I,  outlet  for  distilled  water. 

The  so-called  "dry"  or  destructive  distillation  consists 
of  heating  solid  substances  in  tightly  closed  vessels, 
i.  e.,  in  the  absence  of  air.  It  is  a  chemical  process, 


HEAT  III 

the  substance  being  broken  up  and  other  substances 
formed. 

Distillation  is  used  to  free  a  liquid  from  some  sub- 
stance dissolved  in  it,  since  the  liquid  alone  vaporizes, 
the  solid  matter  needing  a  much  greater  degree  of  heat 
to  drive  its  molecules  apart. 

When  a  mixture  of  liquids  or  a  solution  of  solid  matter 
in  one  or  more  liquids  is  heated,  the  most  "volatile  (that  is, 
the  one  which  boils  at  the  lowest  temperature)  is  naturally 
the  first  to  be  vaporized.  For  example,  if  a  mixture  of 
ether  and  water  be  heated,  the  ether  will  be  evaporated 
and  disappear  long  before  the  water  begins  to  boil. 
In  this  way  liquids  that  have  different  boiling-points 
may  be  separated  and  purified  by  distillation.1 

Distilled  water  is  absolutely  pure,  since  it  has  by  the  process 
undergone  been  freed  from  any  matter  dissolved  in  it.  Water 
from  a  well,  a  river,  or  a  lake  may  be  pure  in  the  sense  that  it  has 
no  harmful  matter  in  it,  but  since  it  usually  has  in  solution  some 
mineral  or  other  matter,  it  is  not  pure  in  the  chemical  or  scientific 
sense.  Stills  are  sometimes  attached  to  water  sterilizers  so  that 
the  water  may  be  distilled,  and  so  freed  from  all  mineral  as  well  as 
vegetable  or  animal  impurities. 

SUMMARY 

Heat  is  molecular  motion,  probably  a  species  of  vibra- 
tion. When  the  molecules  are  moving  very  rapidly, 
the  substance  is  said  to  be  hot;  when  less  rapidly, 
warm;  when  still  less  rapidly,  cool  or  cold. 

1  An  interesting  example  of  this  occurs  in  the  manufacture  of 
petroleum  products.  Benzine,  being  very  volatile,  is  the  first  to 
be  collected  in  the  process  of  distillation,  then  gasoline,  then  kero- 
sene, and  so  on. 


112  PRACTICAL  PHYSICS  FOR  NURSES 

The  chief  source  of  heat  is  the  sun.  Heat  is  also  pro- 
duced by  friction,  by  percussion,  by  chemical  and  by 
electric  action.  Bodily  heat  is  the  result  of  the  chem- 
ical processes  occurring  in  nutrition,  of  muscular  action, 
the  circulation,  etc.  It  is  lost  by  radiation  and  evapo- 
ration. 

Normal  temperature  is  the  condition  of  balance  be- 
tween production  and  loss  of  heat.  High  temperature 
is  the  result  of  overproduction  or  insufficient  elimination 
or  radiation  of  heat.  Subnormal  temperature  is  usually 
due  to  underproduction  of  heat. 

Burning  is  a  chemical  process  in  which  matter  changes 
not  merely  its  form,  but  its  actual  composition  and 
hence  its  identity. 

Temperature  is  degree  of  heat.  The  terms  "warm" 
and  "cold"  are  relative,  and  our  sensations  are  not 
sufficiently  accurate  to  judge  of  them. 

Heat  produces  five  general  effects:  rise  in  tempera- 
ture, increase  in  volume,  increase  of  pressure,  in  the 
container,  change  in  state,  or  change  in  character. 

Heat  expands  substances.  Cold  contracts  them. 
Water  is  the  marked  exception  to  this  rule,  in  that  it 
expands  upon  freezing. 

Uneven  expansion  or  contraction  causes  breakage  in 
brittle  substances. 

The  thermometer  is  a  device  for  the  accurate  measure- 
ment of  the  degree  of  heat.  The  clinical  thermometer 
is  made  with  a  contraction  in  the  tube  which  prevents 


HEAT  113 

the  mercury  from  returning  to  the  bulb  unless  shaken 
back. 

In  the  Centigrade  scale  zero  is  freezing-point,  100° 
boiling-point. 

A  calorie  is  the  amount  of  heat  required  to  raise  1 
pound  of  water  4  degrees  Centigrade  in  temperature. 

In  boiling,  portions  of  water  are  successively  vaporized, 
the  light  steam  rising  in  bubbles,  which  break  at  the 
surface.  The  temperature  at  which  liquids  boil  varies 
greatly.  Water  is  taken  as  the  standard. 

Dissolving  a  substance  in  water  raises  the  boiling- 
point  of  the  water.  Increase  in  the  air  pressure  upon 
the  surface  of  water  raises  its  boiling-point.  Decrease 
in  the  pressure  lowers  its  boiling-point. 

Dressing  sterilizers  employ  superheated  (dry)  steam 
under  a  pressure  of  15  or  more  pounds;  this  forces  its 
way  into  the  materials  and  the  higher  temperature  ob- 
tained makes  the  bactericidal  action  more  certain. 
Water  sterilizers  boil  the  water  to  render  it  germ  free, 
then  cool  or  reheat  it  as  desired.  Utensil  and  instru- 
ment sterilizers  are  merely  vessels  arranged  conveniently 
for  boiling. 

By  evaporation  liquids  are  changed  into  gases  and 
diffused  into  the  air. 

Evaporation  cools.  In  bathing  or  other  procedures 
to  reduce  temperature  as  much  evaporation  as  possible 
should  be  obtained.  The  evaporation  of  the  perspira- 
tion cools  the  body  under  normal  circumstances. 


114  PRACTICAL  PHYSICS  FOR  NURSES 

Condensation  is  the  opposite  of  evaporation. 

Distillation  is  the  process  of  vaporizing  a  liquid, 
collecting  the  vapor  and  recondensing  it.  Distillation 
is  used  to  free  liquids  from  impurities  or  to  separate 
liquids  that  have  different  boiling-points.  Only  the 
liquid  vaporizes,  any  solid  substance  in  solution  being 
left  behind.  Distilled  water  is  chemically  pure. 

Dry  distillation  is  a  chemical  process. 


CHAPTER  VIII 
HEAT  (Continued) 

TRANSMISSION  OF  HEAT 

SINCE  heat  is  motion,  we  can  easily  understand  how 
it  may  be  transmitted  from  one  thing  to  another.  There 
are  three  methods  by  which  this  occurs:  conduction, 
convection,  and  radiation.  Conduction  refers  to  solids; 
convection,  to  liquids  and  gases. 

Conduction. — When  one  portion  of  a  solid  body  is 
heated,  its  molecules  transmit  their  motion  to  those 
next  them,  and  the  heat  travels  throughout  the  whole 
body.  In  other  words,  the  heat  is  conducted  from 
one  portion  to  another. 

Substances  differ  greatly  in  their  power  of  conducting 
heat.  Upon  this  fact  many  of  the  conveniences  of  life 
depend,  temperature  being  a  very  large  factor  in  our 
comfort. 

Metals  are,  as  a  rule,  good  conductors  of  heat.  Cloth 
and  most  porous  materials  are  poor  conductors. 

Experiments. — Put  the  end  of  a  short  iron  wire  into  a  flame; 
note  how  soon  the  end  held  by  the  fingers  becomes  hot.  Put  the 
end  of  a  sliver  of  wood  or  a  straw  into  a  flame;  it  burns  close  to  the 
fingers  before  any  heat  is  observed  in  the  straw  itself. 

"5 


Il6  PRACTICAL  PHYSICS  FOR  NURSES 

Flat-iron  handles,  tea-pot  handles,  etc.,  are  made  of 
wood  because  it  is  a  poor  conductor  of  heat.1  A  kitchen 
"holder"  is  merely  a  substance  that  is  a  poor  conductor 
of  heat. 

Wool  is  a  poorer  conductor  of  heat  than  cotton,  cot- 
ton poorer  than  linen.  Linen  clothing  and  bedding 
tend  to  cool  the  body  by  conducting  heat  away  from  it. 
Wool  keeps  the  bodily  heat  to  a  great  extent  where  it 
is.  Cotton  conducts  it  away  but  slowly.  Asbestos, 
which  is  a  very  poor  conductor  of  heat,  is  used  for  cover- 
ing steam-pipes  when  we  wish  to  keep  their  heat  from 
escaping. 

Wool  is  used  for  fomentation  cloths  because  it  is  a 
poor  conductor  of  heat  and  so  retains  it  for  a  long  time. 
Cotton  fomentation  cloths  give  up  their  heat  quickly 
and  so  are  not  satisfactory. 

Water  is  a  poor  conductor  of  heat. 

Experiment. — Hold  a  test-tube  nearly  filled  with  water  by  its 
bottom  and  heat  the  top  of  the  water  in  a  flame;  the  top  will  boil 
while  the  bottom  is  barely  warmed. 

Large  bodies  of  water  tend  to  keep  the  temperature 
of  the  ah*  in  their  vicinity  even.  Towns  built  near  a 
large  body  of  water  are  not  as  likely  to  be  hot  in  summer 
as  corresponding  inland  towns,  while  in  winter  they  are 
often  warmer.  Farmers  on  the  shores  of  the  great  lakes 

1  The  so-called  "cold  handle,"  though  made  of  metal,  is  ar- 
ranged so  that  heat  must  travel  a  long  way;  the  handle  becomes 
"air-cooled"  in  the  process. 


HEAT  117 

find  that  the  lake  keeps  away  frost  by  preventing  sudden 
drops  in  temperature.  (Other  factors,  of  course,  modify 
this  general  rule.) 

Air  and  all  gases  are  poor  conductors  of  heat  because 
their  molecules  are  so  far  apart  that  they  do  not  readily 
convey  their  motion  to  their  neighbors.  Much  practical 
use  is  made  of  this  fact. 

It  is  well  known  that  loose  clothing  keeps  the  body 
warmer  than  tight  clothing,  not  only  because  the  cir- 
culation is  less  impeded,  but  because  it  encloses  a 
considerable  quantity  of  air  which  does  not  conduct 
the  bodily  heat  away.  Several  layers  of  light  clothing 
are  warmer  than  few  heavier  ones  because  of  the  layers 
of  air  between  them. 

If  a  house  be  built  with  a  double  wall,  having  an  air 
space  between  the  two  parts,  it  will  be  warmer  in  winter 
and  cooler  in  summer  than  one  built  with  a.  solid  wall 
twice  as  thick.  Double  windows  keep  heat  in  because 
of  the  air  enclosed  between  them. 

Refrigerators  are  devices  for  keeping  out  heat  as  well 
as  for  retaining  cold.  (Cold  is  merely  absence  of  heat.) 
Their  walls  are  made  of  materials  which  are  poor  con- 
ductors of  heat,  as  wood,  paper,  cork,  sawdust,  air.  It 
is  the  number  and  thickness  as  well  as  the  particular 
material  of  these  layers  that  makes  a  refrigerator  a 
good  one.  In  choosing  a  refrigerator,  one  with  thick 
walls  is  pretty  certain  to  be  better  than  one  with  thin 
walls.  In  ice-houses  the  walls  usually  have  large 


118 


PRACTICAL  PHYSICS  FOR  NURSES 


"dead  air"  spaces,  since  air  which  cannot  be  disturbed 
prevents  the  passage  of  heat  very  effectively. 


iP 

vj 

^J 

1 

1 

MINERAL 
WOOL 

1 

1 

1 

I 

ct 

1 

r    ~'^s— 

r*- 

1 

Sheathing. 


Fig.  46. — Section  of  a  refrigerator  wall  (Butler,  "Household 
Physics"). 

(There  should  be  circulation  of  air  in  the  interior  of  a  refrigera- 
tor. The  ice  is  always  placed  at  the  top;  it  cools  the  air  there,  which 
drops  because  of  its  weight  and  because  it  is  pushed  aside  by  the 
lighter,  warmer  air  below.  This  warmer  air,  in  turn,  becomes 
cool  and  drops;  thus  a  circulation  is  maintained,  keeping  the  food 
cold.  Any  food  having  a  pronounced  odor  should  be  kept  in  a 
separate  tight  compartment,  or  any  food  like  butter  or  milk  which 
readily  absorbs  odors.) 

One  can  keep  ice  for  a  considerable  length  of  time  by 
wrapping  it  in  a  woolen  cloth  and  hanging  it  in  the  air. 
In  the  refrigerator,  however,  the  object  is  not  to  keep  the 
ice,  but  to  cool  the  food.  Ice  in  a  refrigerator  should, 
therefore,  be  left  uncovered. 


HEAT 


119 


Capacity  for  Heat. — If  a  substance  is  a  poor  conductor 
of  heat,  it  follows  that  it  holds  or  retains  heat  for  a 
longer  time  than  does  a  substance  which  is  a  good  con- 
ductor of  heat.  Hot-water  bottles  are  of  advantage 
because  the  water  retains  its  heat  so  well.  Bricks  or 
stones  hold  heat  well.  Stove-lids  or  other  metal  articles 
impart  their  heat  quickly  to  objects  that  are  in  contact 
with  them,  and  so  become  cool  themselves.  The  best 


Fig.  47. — Circulation  of  air  in  a  refrigerator  (Butler,  "Household 
Physics"). 

heater  is  a  stone  jug  of  water,  because  both  water  and 
stone  are  poor  conductors  of  heat,  i.  e.,  retain  heat  well. 
The  fireless  cooker  is  a  device  that  makes  use  of  sub- 
stances which  are  poor  conductors  of  heat,  such  as  as- 
bestos, felt,  dead  air,  hay,  etc.,  to  prevent  heat  from  es- 
caping from  the  contents  of  a  vessel  which  has  been 
heated  to  boiling-point.  The  apparatus  keeps  the  food 
at  a  temperature  somewhat  less  than  boiling-point, 
but  sufficiently  high  to  continue  the  cooking  process. 


120 


PRACTICAL  PHYSICS  FOR  NURSES 


If,  in  addition,  heated  soapstone  disks  are  laid  over  the 
food  containers,  still  more  heat  is  retained  and  further 
cooking  made  possible. 

The  vacuum  bottle  has  a  space  in  its  wall  from  which 
some  of  the  air  has  been  withdrawn,  leaving  a  partial 
vacuum;  this  leaves  so  few  molecules  of  air  in  the  con- 
fined space  that  (in  addition  to  the  fact  that  they  .are 


nner  Bottfe 
Outer  Bottle 
Outer  Casing 


Fig.  48. — Section  ol  vacuum  bottle  (Butler,  "Household  Physics"). 

confined)  they  do  not  transmit  their  motion  to  one 
another  nor  to  their  surroundings  except  with  the 
greatest  difficulty.  By  this  means  heat  within  the 
bottle  is  kept  in;  or  if  it  is  desired  to  keep  the  contents 
cold,  the  outside  heat  is  prevented  from  getting  in. 

Convection  is  the  movement  of  liquids  or  gases  by 
means  of  which  heat  is  distributed  through  them.    Air 


HEAT 


or  water  heated  at  the  bottom  starts  rapid  currents  of 
convection,  because  the  heated  portion  is  lighter  and  so 
rises,  stirring  the  whole  mass.  We  have  seen  that 
water  may  be  heated  to  boiling  at  the  top  without 
marked  effect  upon  that  below;  boiling  would  be  almost 
impossible  if  we  applied  heat  only  at  the  top. 

Experiments. — Water:  Put  a  small  quantity  of  sawdust  into 
water;  apply  heat  to  the  bottom  ol  the  container  and  watch  the 
convection  currents.  Air:  Repeat  the  experiment  given  on  page 
92.  This  illustrates  the  convection  of  gases. 


Fig.    49. — Convection    currents    in     water     (Butler,     "Household 
Physics"). 

Plumbing  and  Heating. — The  principle  of  convection 
in  liquids  and  gases  underlies  most  of  our  arrangements 
for  plumbing  and  heating. 


122 


PRACTICAL  PHYSICS  FOR  NURSES 


Hot  water,  being  lighter,  always  rises.  When  we  use 
the  kitchen  range  for  supplying  hot  water  the  arrange- 
ment is  as  follows:  The  cold  water  enters  the  "water- 
back"  of  the  range  (a  flat  thin  tank  set  next  to  the  fire 
so  as  to  expose  a  large  surface  to  be  heated)  from  the 
bottom  of  the  tank  in  the  kitchen.1  As  it  becomes 


Fig.  50. — Heating  water  with  kitchen  range  (Butler,  "Household 
Physics"). 

heated,  it  rises  through  the  pipe  which  discharges  near 
the  middle  of  the  tank.  From  here  it  continues  to  rise, 
the  hottest  water  always  being  at  the  top  of  the  tank. 

1  This  tank  is  incorrectly  called  a  boiler. 


HEAT  123 

It  circulates  by  means  of  a  pipe  branching  to  all  the 


Fig.  51. — Hot-water  heating  system  (Butler,  "Household  Physics"), 
fixtures  in  the  house,  where  it  is  drawn  off  at  the  faucets. 


124  PRACTICAL  PHYSICS  FOR  NURSES 

The  supply  is  kept  renewed  by  the  entrance  of  cold 
water  into  the  tank. 

When  hot  water  is  supplied  from  a  tank  connected 
with  the  heating  system  and  heated  by  it,  the  principle 
of  convection  is  the  same. 

A  hot-water  heating  system  is  arranged  so  that  water 
heated  in  a  boiler  in  the  basement  rises  through  pipes 
and  circulates  in  radiators  placed  in  the  various  rooms. 
As  it  cools  in  the  radiators  it  falls,  and  so  returns  to  the 
heater.  Since  hot  water  expands  so  greatly,  such  a 
system  must  be  provided  \\ith  an  expansion  tank  at 
its  highest  point  (usually  in  the  attic)  into  which  the 
excess  of  hot  water  runs.  If  the  pipes  were  not  provided 
with  this  outlet  they  would  burst  when  the  water  was 
heated. 

Steam  heating  systems  take  advantage  of  the  law  of 
expansion  of  gases.  Steam  set  free  from  a  boiler  in  the 
basement  rises  and  struggles  to  escape.  It  forces  its 
way  through  the  pipes  provided  for  it  into  the  radiators. 
There  it  gives  up  its  heat,  cools,  and  in  consequence 
condenses,  falling  to  the  bottom  and  dripping  through 
the  "return"  pipe  back  to  the  basement.  It  re-enters 
the  boiler  as  cold  water,  coming  in  at  the  bottom,  and 
again  ascending  as  it  is  heated  and  changed  into 
steam. 

(It  can  be  readily  seen  that  the  heat  from  steam  is  much  more 
intense  than  that  from  hot  water;  to  this  is  due  the  almost  universal 
overheating  of  buildings  where  the  former  is  used.) 


HEAT 


125 


Radiation  of  Heat. — A  heated  body  starts  in  the  air 
about  it  molecular  movements  which  radiate  or  move 
in  all  directions;  by  this  means  it  loses  its  heat,  trans- 
mitting it  to  the  air  and  thence  to  surrounding  objects. 
The  heat  of  a  fire  literally  strikes  your  face  or  body  when 
you  are  near  it. 


Fig.  52. — Steam  heating  system  (Butler,  "Household  Physics"). 

Hold  your  hand  between  your  face  and  a  fire,  and  the 
heat  is  shut  off  from  your  face.  Why?  Because  you 
have  intercepted  the  waves  of  molecular  motion  which 
were  coming  from  the  fire. 

Radiation  takes  place  slowly  from  smooth  surfaces, 
more  rapidly  from  rough  ones.  Is  it  for  this  reason 


126  PRACTICAL  PHYSICS  FOR  NURSES 

that  objects  which  we  wish  to  have  retain  their  heat 
are  made  smooth  (as  the  tea-kettle,  hot-water  bottle, 
etc.),  while  those  which  we  wish  to  give  up  their  heat 
rapidly  are  rough  (as  stoves,  steam  radiators,  etc.). 

Steam  or  hot-water  radiators  are  exactly  what  their 
name  implies.  They  are  hot  bodies  which  start  heat 
movements  in  the  air  about  them.  The  larger  their 
surface,  the  more  heat  they  radiate  or  give  off;  this  is 
the  reason  for  making  them  in  the  usual  form,  with  many 
pipes,  thus  presenting  a  large  surface  which  is  in  con- 
tact with  the  air.  If  they  were  flat  boxes  they  would 
need  to  be  very  much  larger  in  order  to  present  the  same 
amount  of  radiating  surface.  Hospital  engineers  object 
to  having  the  radiators  in  an  operating  room  covered 
with  sheets,  because  it  makes  them  in  effect  a  flat  box  and 
reduces  the  actual  radiating  surface  so  greatly  that  it 
becomes  impossible  to  heat  the  room. 

Radiators  are  commonly  placed  at  the  bottom  of  the 
room  and  in  its  coldest  part,  i.  e.,  next  the  windows,  so 
that  they  may  start  convection  currents  of -warm  air 
in  the  portion  where  it  is  most  needed  and  the  room  be 
heated  more  evenly. 

The  human  body  is  of  a  higher  temperature  than  the 
air  which  usually  surrounds  it.  It  therefore  radiates 
its  heat.  If  heat  were  not  constantly  being  produced 
in  the  body1  we  should  become  cold  from  the  mere  fact 
of  radiation.  Other  conditions  being  equal,  small 
1  Much  of  the  bodily  heat  is  produced  by  chemical  action. 


HEAT  127 

persons — presenting  a  larger  surface  in  proportion  for 
radiation — tend  to  lose  their  heat  more  rapidly  than  do 
large  persons;  for  this  reason  it  is  necessary  to  protect 
babies  from  sudden  cooling. 

Clothing,  especially  that  made  of  materials  which  are 
poor  conductors  of  heat  (as  wool),  prevents  radiation  of 
bodily  heat,  and  so  keeps  the  body  warm.  On  the  other 
hand,  thin  clothing,  or  that  made  of  materials  which  are 
good  conductors  of  heat  (as  linen),  allows  the  bodily 
heat  to  radiate  and  so  be  lost.  Thin  clothing  also  per- 
mits rapid  evaporation  of  perspiration,  which  assists 
the  cooling  process. 

Sunstroke  occurs  as  follows:  The  high  temperature  of 
the  surrounding  air  practically  abolishes  both  radiation 
and  conduction  of  heat.  If,  in  addition,  there  be  high 
humidity,  so  that  evaporation  from  the  skin  is  also 
stopped,  while  heat  production  in  the  body  continues, 
excessive  elevation  of  bodily  temperature  takes  place, 
and  sunstroke  is  the  result. 

LATENT  HEAT 

When  heat  goes  into  a  substance,  yet  does  not  change 
its  temperature,  it  is  called  latent  (hidden)  heat. 

Experiments. — (a)  Put  cracked  ice  into  a  small  vessel,  set  a 
thermometer  in  it  (keeping  the  bulb  of  the  thermometer  off  the 
bottom),  and  apply  heat.  The  thermometer  registers  the  same 
temperature,  just  above  freezing-point,  until  all  the  ice  is  melted. 
(b)  Boil  water  for  ten  minutes,  testing  with  the  thermometer. 
The  water  is  changed  to  steam,  yet  gets  no  hotter  than  212°  F.  In 
each  case  we  are  sure  that  heat  is  entering  the  vessel  and  contents, 
yet  we  find  no  record  of  it. 


128  PRACTICAL  PHYSICS  FOR  NURSES 

Latent  heat  is  that  which  disappears  when  a  substance 
changes  its  form. 

The  explanation  is  as  follows:  The  molecules  in  either 
solids  or  liquids,  being  held  together  by  cohesion,  take 
considerable  force,  or  energy,  to  separate  them.  The 
heat  energy  which  we  put  into  them  in  the  process  of 
heating  is  used  in  overcoming  this  cohesion  and  enabling 
them  to  change  their  form. 

Artificial  Cold. — It  should  be,  and  is,  possible  to  re- 
cover this  lost  energy.  It  is  done  by  reversing  the 
process  of  liquefaction  or  evaporation.  Water  under 
normal  conditions  freezes  very  slowly  because  it  takes 
time  to  get  rid  of  the  latent  heat  or  energy  which  it 
acquired  upon  liquefying.  If  we  wish  to  make  ice 
artificially  and  rapidly,  we  hasten  the  process  by  rapidly 
vaporizing  some  volatile  liquid,  such  as  ammonia  or 
compressed  carbon  dioxid;  it  extracts  heat  for  this 
change  from  water  which  is  placed  adjoining  it;  the 
water,  therefore,  freezes. 

In  freezing  ice-cream,  the  salt  hastens  the  melting  of 
the  ice,  causing  it  to  extract  heat  from  any  nearby  object, 
which  in  this  case  happens  to  be  the  cream. 

SUMMARY 

Solids  conduct  or  radiate  heat.  Liquids  or  gases  con- 
vey it  by  currents.  Conduction,  convection,  and  radia- 
tion are  all  modes  of  transference  of  molecular  motion. 

Metals  are,  as  a  rule,  good  conductors  of  heat.    Wood, 


HEAT  129 

wool,  etc.,  are  poor  conductors.  Water  is  not  a  good 
conductor  of  heat,  nor  is  air.  We  choose  our  clothing, 
and  utensils,  build  our  homes,  etc.,  with  reference  to 
these  qualities  in  materials.  The  hot-water  bottle,  fo- 
mentation flannels,  double  windows,  the  fireless  cooker, 
the  vacuum  bottle,  refrigerators,  etc.,  are  examples 
of  the  practical  application  of  the  principles  of  heat 
conduction  and  radiation. 

Objects  which  conduct  heat  poorly  hold  it  well,  and 
vice  versa. 

Convection  of  heat  by  currents  of  water  or  air  is  the 
underlying  principle  of  our  heating,  ventilating,  and 
hot-water  supply  systems. 

Objects  give  off  heat  by  radiation  from  their  surface. 
Rough  surfaces  radiate  better  than  smooth  ones. 

The  human  body  loses  heat  by  radiation.  Clothing 
tends  to  prevent  this  loss. 

Sunstroke  is  due  to  lack  of  heat  radiation  and  evapora- 
tion of  the  perspiration,  coupled  with  excessive  heat 
production. 

During  boiling  and  melting  no  change  in  temperature 
takes  place,  even  though  heat  is  constantly  entering  the 
substance  under  observation.  This  heat  which  is 
apparently  lost  and  produces  no  effect  is  called  latent 
heat.  It  may  be  recovered  by  reversing  the  processes. 


CHAPTER  IX 
SOUND 

What  Sound  Is.— Drop  a  pebble  into  a  pool  of  still 
water.  It  starts  small  waves  or  movements  which  travel 
in  all  directions  and  which  strike  the  shore  or  rim  with 
a  definite  force. 

We  live  in  what  is  practically  a  lake  of  air.  Any  dis- 
turbance in  the  air  creates  waves  which  travel  con- 
siderable distances,  until  their  force  expends  itself. 
The  sort  of  air  disturbance  with  which  we  are  most 
familiar  is  sound.  There  has  always  been  much  dis- 
cussion as  to  whether  sound  was  the  air  wave  itself  or 
the  effect  produced  by  it  upon  the  ear  and  brain;  the 
latter  is  now  regarded  as  correct. 

Production  of  Sound. — Sound  is  produced  by  the 
vibration  of  bodies.  Such  bodies  may  be  strings,  mem- 
branes, thin  plates,  etc.  The  vibration  may  be  pro- 
duced by  a  current  of  air,  a  blow,  etc.  In  some  in- 
stances the  vibrations  may  be  felt  or  seen.  Place  your 
hand  lightly  against  a  large  bell  that  has  just  been  rung; 
note  that  the  sound  ceases  when  your  hand  checks  the 
vibration. 

Sound  waves  travel  outward  in  every  direction,  not 
only  on  a  plane,  as  those  in  water  do,  but  up  and  down 
130 


SOUND  131 

also,  along  all  possible  radii  of  a  sphere  whose  center 
is  the  spot  where  the  vibrations  are  produced.  Each 
wave-like  vibration  compresses  the  air  ahead  of  it,  press- 


Fig-  53- — Sound  wave  movement  (Butler,  "Household  Physics"). 

ing  the  molecules  closer  together;  these  rebound,  coming 
wider  apart;  the  rebound  produces  pressure,  the  pres- 
sure a  rebound,  and  so  on;  thus  the  vibratory  move- 
ment consists  of  an  alternate  condensation  and  rare- 
faction of  the  sound  medium.  The  molecules  of  air 
do  not  travel  in  carrying  a  sound,  but  merely  vibrate 
to  and  fro. 


Fig.  54. — Diagram  of  sound  waves. 

Upon  the  amplitude  of  such  vibrations  depends  the 
intensity  and  pitch  of  the  sound. 


132 


PRACTICAL  PHYSICS  FOR  NURSES 


The  Human  Voice  is  produced  by  the  vibrations  of  the 
vocal  cords.  The  vocal  cords  of  the  human  throat 
resemble  strings  or  bands.  They  are  pulled  together 
or  separated,  tightened  or  loosened,  by  muscular  action 


ABC 

Fig-  55- — Top  view  of  larynx:  A,  small  or  highest  register;  B,  upper 
thin  or  middle  register;  C,  lower  thin  or  middle  register. 

(voluntary).  Air  from  the  lungs  is  forced  across  them, 
between  them,  making  them  vibrate.  Low  tones  are 
produced  by  relaxation  of  the  muscles  which  control 
them;  high  tones,  by  tightening. 


Fig-  56- — How  voice  is  modified  (Butler,  "Household  Physics"). 

The  voice  is  modified  by  the  movements  of  the  cords 
themselves,  the  tongue,  lips,  and  cavity  of  the  mouth, 
as  well  as  by  the  size  and  shape  of  the  nasal  cavity,  and 
changes  in  the  shape  of  the  throat.  The  whole  process 
is  very  complicated  and  takes  much  practice  to  get  per- 
fect results.  To  a  certain  extent  quality  of  voice  de- 


SOUND  133 

pends  upon  inborn  characteristics,  but  it  is  largely  the 
result  of  training.  Perfect  control  of  breath,  vocal 
cords,  and  the  muscles  of  throat  and  mouth  is  necessary 
for  excellence  in  speaking  or  singing. 

Organs  of  Hearing. — Our  ears  are  the  organs  which 
collect  a  portion  of  the  sound  waves  and  transmit  the 
impression  gained  therefrom  to  the  brain.  The  sound 
waves,  collected  by  the  external  ear,  cause  the  tightly 


Eustachlan 
tube 

Fig-   57- — Transmission   of  sound    by  mechanism  of  ear   (Butler, 
"Household  Physics"). 

stretched  ear  drum  to  vibrate.  This  vibration  is  taken 
up  by  the  chain  of  tiny  bones  in  the  middle  ear  and  trans- 
mitted to  the  fluid  and  otoliths  of  the  inner  ear.  These, 
in  turn,  stimulate  the  tiny  fibers  of  the  endings  of  the 
auditory  nerve,  which  conducts  the  impulse  to  the  brain 
where  its  meaning  is  interpreted.  The  eustachian  tube 
equalizes  the  air  pressure  between  the  middle  ear  and 
the  outside  world. 


134  PRACTICAL  PHYSICS  FOR  NURSES 

Ability  to  distinguish  between  sounds  and  to  know 
their  meaning  is  the  result  of  a  long  process  of  educa- 
tion and  practice. 

Diseased  conditions,  temporary  or  permanent,  in- 
flammatory processes  which  cause  swelling,  pus,  etc., 
interfere  greatly  with  the  transmission  of  sound  by  the 
ear  mechanism,  or  even  stop  it  altogether.  The  ear 
drum  may  be  tightened  or  relaxed  by  disease,  the 
chain  of  ossicles  stiffened,  the  eustachian  tube  blocked 
so  that  there  is  not  a  proper  adjustment  of  air  pressure, 
or  the  inner  ear  or  auditory  nerve  may  be  effected;  any 
of  these  cause  partial  or  complete  deafness. 


Fig.  58. — Megaphone,  showing  reflection  of  sound  (Butler,  "House- 
hold Physics"). 

Artificial  Aids  to  Hearing. — Ear  trumpets  or  conver- 
sation tubes  are  merely  instruments  which  collect  a 
quantity  of  the  waves  of  sound,  intensify  them  (usually 
by  reflection)  and  convey  them  to  the  ear,  thus  producing 
a  greater  vibration  of  the  ear  drum  than  would  the  few 
waves  which  come  in  ordinary  circumstances.1  The 

1  Other  devices  for  the  deaf  are  in  the   form  of  telephones. 
(See  Chapter  XI.) 


SOUND  135 

megaphone  is  similar;  it  not  only  collects,  but  greatly 
reflects  and  intensifies  the  waves  of  sound. 

Speed  of  Sound. — Sound  waves  move  through  the 
air  at  a  rate  of  1125  feet  per  second.  The  rate  varies 
slightly  with  the  temperature  of  the  air,  with  its  humid- 
ity, density,  etc. 

Sound  travels  much  more  slowly  than  does  light. 
Witness  the  well-known  facts  that  you  see  a  gun  fired 
long  before  you  hear  its  report,  or  that  you  see  a  work- 
man at  a  distance  strike  a  blow  long  before  you  hear  it, 
or  that  lightning  and  thunder — which  are  practically 
simultaneous — sometimes  appear  to  be  far  apart. 

Conduction  of  Sound. — Sound  waves  are  transmitted 
more  readily  by  other  substances  than  by  air.  They 
move  through  water  four  times  as  fast  as  through  air, 
through  wood  ten  times  as  fast,  through  steel  fifteen 
times  as  fast. 

Water,  the  earth,  wood,  metal,  etc.,  are,  therefore, 
better  conductors  of  sound  than  is  air. 

Experiments. — Place  the  ear  at  one  end  of  a  long  table  or  board 
and  listen  for  the  tick  of  a  watch  at  the  other  end;  it  can  be  heard 
at  a  considerably  greater  distance  than  it  can  through  the  air. 
Scratch  with  the  finger  or  a  pin  on  a  table  to  which  the  ear  is  ap- 
plied; the  sound  is  much  louder  than  when  it  comes  through  the 
air.  Listen  to  approaching  footsteps  or  wheels  by  placing  your 
ear  to  the  ground;  they  will  be  heard  long  before  it  is  possible  to 
detect  them  through  the  air. 

The  stethoscope  takes  advantage  of  this.  It  collects, 
by  means  of  a  wide  tube  and  a  vibrating  membrane, 


136  PRACTICAL  PHYSICS  FOR  NURSES 

the  waves  of  sound  made  by  the  action  of  heart  or  lungs, 
conducting  them  to  the  ears  by  means  of  tubes  and 
ear-pieces.  The  phonendoscope  magnifies  or  increases 
the  intensity  of  the  sounds  it  transmits,  and  is  there- 
fore sometimes  preferred  in  making  delicate  distinctions. 

Intensity  of  Sound.— Sounds  differ  greatly  in  in- 
tensity because  of  the  great  variation  in  the  force  of  the 
vibration  that  produces  them.  Intensity  is  influenced 
by  the  medium  of  transmission,  the  nearness  of  the 
hearer,  the  action  of  reflectors,  concentrators,  etc. 

Pitch. — Sounds  differ  in  pitch,  being  high,  low,  or 
medium.  Difference  in  pitch  is  due  to  a  difference  in 
the  number  of  vibrations  per  second  produced  by  the 
object  which  makes  the  sound.  High  pitch  is  due  to 
rapid  vibration;  low  pitch,  to  slower  vibration.  Also, 
small  cords  or  objects  give  tones  of  high  pitch;  large 
ones,  tones  of  low  pitch.  Also,  tightly  stretched  strings 
give  higher  tones  than  loose  ones.  (These  facts  may  be 
verified  by  examining  the  strings  of  a  piano  while  they 
are  being  struck.)  The  human  ear  is  able  to  distinguish 
sounds  having  from  16  to  32,500  vibrations  per  second.1 

This  is  the  reason  that  women  and  children  have 
high-pitched  voices,  because  their  vocal  cords  are  small 
and  light,  and  readily  drawn  tight. 

1  We  are  told  that  there  are  sounds  of  such  extremely  high  pitch 
that  the  human  ear  cannot  respond  to  them.  Animals  and  insects 
undoubtedly  hear  sounds  outside  of  the  range  of  our  ears,  because 
of  the  different  or  more  delicate  construction  of  their  auditory  ap- 
paratus, 


SOUND  137 

Hoarseness  is  due  to  a  swelling  of  the  vocal  cords  or  a 
gathering  of  mucus  between  or  upon  them. 

Reflection  of  Sound. — Sound  waves  are  reflected 
from  any  surface  which  they  strike  (see  Fig.  58) ,  but  not 
noticeably  from  small  or  rough  surfaces,  nor  those  com- 
posed of  soft  or  porous  materials.  If  the  surface  is 
broad,  flat,  and  smooth,  the  reflection  is  more  perfect. 
This  reflection,  or  echo,  coming  from  a  large  surface 
situated  at  an  exact  distance  is  often  very  clear.  In  an 
ordinary  room  there  is  this  same  reflection  of  sound, 
from  walls  and  ceiling,  but  it  comes  so  quickly  after  the 
sound  itself  that  we  hear  them  as  one.  In  large  rooms 
it  may  be  very  annoying.  Fireproof  hospital  buildings 
are  often  troublesome  because  of  their  resonance;  being 
built  of  hard,  smooth  materials  (metals,  hard  plaster, 
etc.)  they  reflect  sound  and  often  even  magnify  it. 

Interference  with  Sound. — To  prevent  sound  waves 
from  traveling  we  block  their  way  by  interposing  a 
different  medium.  A  closed  door  reflects  sounds  rather 
than  transmits  it,  and  only  a  few  waves  go  through 
the  cracks  around  it. 

One  hears  more  easily  indoors  because  the  walls 
keep  the  sound  waves  in,  besides  collecting  and  reflect-, 
ing  them,  so  retaining  or  increasing  their  intensity. 
Out  of  doors,  they  go  off  in  all  directions. 

Sound  waves  lose  their  force  in  passing  a  corner,  so 
that  their  greatest  strength  is  evident  when  the  recipient 
is  directly  in  front  of  the  object  or  person  producing  the 


138  PRACTICAL  PHYSICS  FOR  NURSES 

sound.  For  this  reason  a  nurse  should  stand  or  sit  as 
nearly  as  possible  in  front  of  a  patient  to  whom  she  is 
speaking,  so  that  he  may  hear  her  without  effort. 

Music  and  Noise. — We  distinguish  between  noise  and 
music  as  it  chances  to  be  pleasing  or  displeasing  to  us 
personally.  It  is  agreed,  however,  that  musical  sounds 
are  those  in  which  the  vibrations  are  uniform  and 
regular,  while  noise  is  a  succession  of  confused  and 
irregular  vibrations. 


Fig-  59- — Sound  waves  of  music  and  of  noise. 

Heart  and  Lung  Sounds. — The  sounds  made  by  the 
normal  heart  in  its  contraction  and  relaxation  resemble 
"Lubb,  dup."  If,  for  any  reason,  the  valves  do  not 
close  properly,  blood  gurgles  back  through  them,  pro- 
ducing a  characteristic  sound.  If  the  valve  edges  are 
rough,  or  the  valve  stiffened  by  disease,  the  sound  is 
modified.  By  long  practice  and  experience  physicians 
learn  to  recognize  each  slight  change  in  sound  and  to 
know  its  exact  meaning. 

The  "normal  sound  made  by  the  air  passing  in  and  out 
of  the  lungs  is  like  that  of  a  steady,  gentle  breeze. 
Bronchial  secretion  in  excess  may  cause  a  rattling  sound ; 


SOUND  139 

tough  mucus,  the  sound  called  "rales,"  a  sort  of  whist- 
ling; fluid  in  the  air  cells,  a  gurgling  or  crackling  sound; 
pleurisy  may  give  a  rubbing  sound,  the  "friction  mur- 
mur." Absence  of  sound  where  it  should  be  found 
indicates  consolidation  of  lung  tissue. 

SUMMARY 

Sound  is  vibration  which  stimulates  the  auditory 
nerve.  This  vibration,  due  to  whatever  cause,  produces 
waves  which  travel  outward  in  every  direction.  Upon 
their  size  and  shape  depend  the  quality  of  the  sound 
produced. 

The  human  voice  is  produced  by  the  vibration  of  the 
vocal  cords.  It  is  modified  by  the  muscles  of  the  larynx, 
throat,  and  mouth,  and  by  the  size  and  shape  of  the 
mouth  and  nasal  cavities.  Abnormal  or  diseased  con- 
ditions also  alter  its  quality. 

The  external  ear  collects  sound  waves,  which  cause 
the  ear  drum  to  vibrate.  The  vibration  is  transmitted 
by  the  mechanism  of  the  middle  and  inner  ear  to  the 
auditory  nerve,  thence  to  the  brain,  which,  after  train- 
ing, acts  as  interpreter. 

Devices  for  the  aid  of  the  deaf  collect,  reflect,  and 
increase  the  force  of  sounds. 

Sound  waves  travel  about  1125  feet  per  second  through 
the  air,  and  much  more  rapidly  through  water  or  solid 
materials. 

Sound    waves    are    reflected,    especially    from    hard, 


140  PRACTICAL  PHYSICS  FOR  NURSES 

smooth  surfaces.  A  perfect  reflection  is  called  an  echo. 
Indoors  reflection  of  sound  assists  us  in  hearing,  because 
it  increases  the  force  of  sounds;  but  it  may,  in  a  large 
room,  tend  to  confuse  sounds. 

Sound  waves  may  be  stopped  by  interposing  some 
different  material.  Sound  cannot  travel  around  a 
corner  without  considerable  loss. 

Intensity  of  sound  is  due  to  the  character  of  the 
force  that  produces  it. 

Pitch  is  due  to  the  number  of  vibrations  per  second, 
the  size  of  the  vibrating  object,  etc. 

Music  is  regular  vibration;  noise,  irregular. 

Heart  and  lung  sounds  are  indicative  of  the  condition 
of  these  organs,  but  it  takes  experience  to  interpret 
them  correctly.  Changes  in  or  stiffening  of  the  valves 
of  the  heart  produce  certain  definite  abnormal  sounds. 
The  presence  of  secretion  or  tissue  changes  in  the  lungs 
produce  sounds  that  are  of  diagnostic  value. 


CHAPTER  X 
LIGHT 

What  Light  Is. — Until  about  one  hundred  years  ago 
it  was  thought  that  light  was  a  material  substance 
which  came  from  the  object  seen.  Now  it  has  been 
discovered  that  light  is  similar  to  heat  and  sound,  in 
that  it  is  made  up  of  waves. 

Light  waves  are  about  30000  inch  in  length,  and  they 
move  much  more  rapidly  than  do  the  waves  of  heat  or 
of  sound.  Light  waves  may  be  changed  into  heat 
waves.1 

Transmission  of  Light. — Light  waves  are  transmitted 
not  through  air  nor  through  liquids,  but  through  what 
— for  want  of  a  better  term — we  call  the  ether.  We  do 
not  know  what  the  ether  is,  but  we  know  that  every- 
where, pervading  all  liquids  and  solids,  filling  every 
space  in  the  world,  and  all  the  spaces  between  the  worlds 
and  stars  and  suns,  there  is  something  which  transmits 
light  waves. 

Light  waves  travel  at  the  rate  of  about  185,000  miles 
per  second.  It  can  be  judged  from  this  that  air  is  too 
coarse  a  material  to  transmit  them. 

1  Glass  transmits  light  readily,  heat  with  some  difficulty.  In 
a  cold  frame,  the  light  of  the  sun,  passing  easily  through  the  glass, 
is  absorbed  by  the  earth  and  the  plants  and  turned  into  heat. 
This  heat  is  retained  by  the  glass  and  so  accumulates. 

141 


142  PRACTICAL  PHYSICS  FOR  NURSES 

Sir  Oliver  Lodge,  one  of  the  world's  greatest  scientists, 
considers  that  light  waves  may  be  electric  waves.  An 
important  point  in  support  of  his  opinion  is  that  light 
and  electricity  travel  at  the  same  rate  of  speed.  . 

Direction  of  Light. — Light  waves  always  travel  in 
straight  lines.  They  cannot  turn  a  corner.  We  there- 
fore call  the  direction  of  light  waves  rays,  and  think  of 
light  as  straight  rays  sent  out  in  every  direction  from 
the  luminous  or  illuminated  object. 


Fig.  60. — Direction  of  light  waves.     Light  rays. 

We  see  an  object,  however,  in  the  direction  in  which 
its  light  rays  enter  our  eyes.  For  example,  when  we  look 
at  an  object  reflected  in  a  mirror  we  seem  to  see  it  behind 
the  mirror,  though  we  know  that  it  is  in  front.  Figure 
61  explains  this. 

Intensity  of  Light.— We  know  that  light  becomes 
dimmer  as  it  travels  away  from  its  source.  Figure  62 
explains  why.  0  is  a  source  of  light.  At  the  distance 


LIGHT 


143 


A  a  certain  number  of  rays  fall  on  a  certain  surface; 
at  the  distance  B,  four  times  as  large,  only  the  same 


object 


Fig.  61. — Reflection  in  mirror. 

number  of  rays  fall.    At  C,  a  surface  much  greater, 
the  illumination  is  very  much  less. 


Fig.  62. — Intensity  of  light  according  to  distance. 

How  Materials  Affect  Light. — Light  cannot  pass 
through  some  sorts  of  material  at  all,  but  is  absorbed  by 
them;  such  materials  we  call  opaque.  Material  which 


144 


PRACTICAL  PHYSICS  FOR  NURSES 


transmits  light  easily  is  called  transparent.  Materials 
which  transmit  a  portion  of  the  light  which  comes  to 
them,  reflecting  the  rest,  are  translucent.  Other  mate- 
rials reflect  all  the  light  which  comes  to  them. 


Fig.  63. — Formation  of  a  shadow:    A,  Source  of  light;  B,  object; 
,  umbra  or  shadow. 

Shadows. — When  rays  of  light  strike  an  opaque 
body,  a  shadow  is  formed  behind  it.  (The  technical 
name  is  umbra.)  If  the  source  of  light  is  small  in  corn- 


Fig.  64. — Formation  of  penumbra:    A,  Source  of  light;  B,  object; 
C,  umbra;  D,  penumbra. 

parison  with  the  size  of  the  object,  the  edge  of  the 
shadow  is  sharp.  If  the  source  of  light  is  large  in  com- 
parison, the  edge  is  blurred.  There  may  be  a  distinct 
band  which  is  dimly  lit,  called  the  penumbra  (Fig.  64). 


LIGHT 


145 


How  We  See. — Light  waves  enter  the  eye,  and  pass 
through  the  cornea,  the  pupil,  the  lens,  and  the  vitreous 
humor,  being  modified  by  each  of  them.  They  strike 
the  retina,  which  is  the  sensitive  portion  that  receives 
the  image.  The  retina  transfers  the  sensation  to  the 
optic  nerve,  which  sends  it  on  to  the  brain  for  inter- 
pretation. 


OPT/C 


-Vitreous  humor 
Fig.  65. — Section  of  the  eye  (Butler,  "Household  Physics"). 

What  We  See. — We  see  only  those  objects  from  which 
light  comes  to  us.  This  light  may  be  given  out  by  the 
object  itself  or  reflected  by  it. 

A  body  that  gives  out  light  is  called  luminous.  The 
sun,  a  fire,  an  electric  light,  a  red-hot  or  white-hot  piece 
of  metal,  etc.,  are  luminous.  That  is,  they  send  out 
waves  of  light.  When  these  waves  enter  the  eye,  we 
see  the  object. 

Most  objects  are  seen,  however,   by  reflected  light. 


146  PRACTICAL  PHYSICS  FOR  NURSES 

Light  from  a  luminous  object,  usually  the  sun  or  an 
artificial  light,  falls  on  the  object  and  is  reflected,  just 
as  sound  is,  or  as  a  rubber  ball  bounds  back  when  thrown 
against  a  wall.  When  we  see  an  object  by  the  light  that 
it  reflects  we  say  that  it  is  illuminated. 

Reflection  of  Light. — All  surfaces  reflect  light  to  some 
extent,  but  in  most  cases  it  is  hardly  noticeable.  Smooth 
surfaces  reflect  light  better  than  rough.  Silvered  glass, 
forming  a  mirror,  is  one  of  the  best. 


Fig.  66. — Reflection  of  light. 

Figure  66  shows  how  reflection  of  light  occurs.  If  the 
light  strikes  the  reflecting  surface  at  an  angle,  it  is  thrown 
off  or  reflected  at  an  exactly  corresponding  angle.  Only 
when  light  strikes  a  reflecting  surface  at  a  right  angle 
does  it  come  back  in  exactly  the  same  direction  from 
which  it  came.  This  law  of  reflection  enables  us  to 


LIGHT 


147 


illuminate  objects  in  positions  where  we  cannot  throw  a 
direct  light  upon  them. 


v 

\ 

7 

^ 

L 

\ 

L 

/ 

Fig.  67. — Seeing  through  a  brick:   B,  Brick  or  other  object;  M,  M, 
M,  M,  mirrors;  L,  L,  L,  light  ray. 

Rays  of  light  may  be  reflected  two  or  more  times, 
and  if  the  material  of  the  reflecting  surface  is  of  the  req- 
uisite quality,  it  may  not  lose  much  in  the  transfer. 


Fig.  68. — Concave  reflector. 

Figure  67  shows  how,  by  means  of  reflecting  mirrors, 
we  may  "see  through  a  brick." 


148  PRACTICAL  PHYSICS  FOR  NURSES 

Reflectors  placed  behind  lights  are  made  smooth  and 
concave,  so  that  they  not  only  collect  and  reflect  the 
light,  but  intensify  it. 

REFRACTION 

Whenever  a  ray  of  light  passes  obliquely  from  one 
transparent  substance  to  another,  it  is  bent  in  its  course. 
This  bending  we  call  refraction. 


Fig.  69. — Refraction  of  light  by  water:    R,  Ray  of  light;  R-A,  line 
of  sight ;  R-B,  refracted  ray. 

Experiments. — Thrust  a  stick  into  a  dish  of  water  at  an  angle, 
and  look  at  it  from  one  side.  It  appears  bent.  Place  a  coin  in  a 
dish  in  such  a  position  that  it  is  just  hidden  by  the  rim;  have  some 
one  pour  water  into  the  dish;  the  coin  will  be  seen.  In  each  in- 
stance the  surface  of  the  water  refracts  or  bends  the  rays  of  light 
coming  from  the  object. 

When  light  enters  a  thick  plate  of  glass,  it  is  bent 
(refracted)  by  the  first  surface  which  it  encounters; 
as  it  passes  through  and  leaves  the  glass  from  the  other 
side,  it  is  bent  again,  always  in  the  same  direction, 
providing  both  surfaces  of  the  glass  are  parallel. 


LIGHT 


149 


Experiments. — Look  at  a  pencil  obliquely  through  a  thick 
piece  of  glass;  it  appears  in  a  different  position  from  what  it  is  known 
to  occupy.  Look  at  a  candle  flame  through  a  square  bottle  filled 
with  water  and  held  diagonally;  the  flame  appears  to  be  much 
higher  than  it  really  is. 


GLftSS 


Fig.  70. — Refraction  of  light  by  glass:    R,  Ray  of  light;  R-A,  line 
ot  sight;  R -B,  refracted  ray. 

Lenses  are  pieces  of  glass  used  for  bending  light  rays. 
Their  surfaces  are  usually  curved,  so  that  light  passing 

Converging       L«OM»  Q, merging     L«n3«a  -;  "g    f 

'i!  il  I!  'i!  Jj  JJ'U    II  J! 


Fig.  71. — Types  of  lenses  (Butler,  "Household  Physics"). 

through  them  may  be  distributed  or  concentrated,  as 
the  case  may  require.     They  may  be  concave  or  convex, 


150  PRACTICAL  PHYSICS  FOR  NURSES 

a  combination  of  the  two,  or  combined  with  a  plane 
surface.  Figure  71  gives  some  of  the  common  forms  of 
lenses. 

Convex  lenses  refract  rays  of  light  so  as  to  cause  them 
to  come  together. 


Fig.  72. — Refractions  of  light  by  convex  lens. 

Experiment. — Hold  a  strong  reading  glass  (a  "burning  glass" 
so  called,  if  it  can  be  obtained)  over  a  sheet  of  white  paper.  Find 
the  distance  at  which  it  gives  the  most  concentrated  light.  The 
glare  is  almost  blinding,  and  the  illuminated  spot  upon  the  paper 
may  scorch,  smoke,  or  even  take  fire.  The  same  effect  can  be  had 
with  a  piece  of  ice  carefully  molded. 


ig-  73-  —  Refractions  of  light  by  concave  lens. 


Concave  lenses  refract  rays  of  light  so  as  to  cause 
them  to  be  distributed. 

Focus.  —  A  convex  lens  whose  curves  are  perfectly 
even  on  all  sides  brings  the  rays  of  light  together  at  a 


LIGHT  151 

point.  This  point  is  called  the  focus  (see  Fig.  72). 
If  we  are  looking  through  the  lens,  it  is  at  this  point 
that  the  image  of  the  object  which  we  are  observing 
appears  distinct  and  clear  cut. 

Polarization. — Light  is  said  to  be  polarized  when  its 
vibrations  are  made  to  take  place  in  one  direction,  and 
its  rays  become  parallel.  Polarization  occurs  by  re- 
flection from  a  mirror,  or  by  refraction.  Certain  trans- 
parent materials  polarize  light  in  a  special  way,  turning 
the  rays  always  toward  the  right  or  toward  the  left, 
as  the  case  may  be.  Tourmaline  is  one  of  these. 

Solutions  of  glucose  (grape-sugar)  polarize  light, 
turning  the  ray  always  to  the  right;  the  degree  of  rota- 
tion is  in  proportion  to  the  amount  of  glucose  present 
in  the  solution.  Levulose  (also  called  fructose)  also 
polarizes  light,  turning  the  ray  to  the  left.  These 
phenomema  are  made  use  of  in  urinalysis  to  determine 
the  character  and  amount  of  sugar  present. 

THE  EYE 

The  cornea  of  the  eye  is  a  convex  lens  which  bends  the 
rays  :f  light  that  enter  it,  bringing  them  closer  together. 
The  lens  of  the  eye,  situated  a  little  behind  the  cornea, 
is  a  double  convex  lens  which  bends  them  twice  more, 
bringing  them  still  further  together.  It  is  by  means 
of  this  arrangement  that  our  eyes  are  able  to  "take  in" 
so  much  at  one  time. 

The  normal  eye  is  so  constructed  that  its  focus,  the 


152  PRACTICAL  PHYSICS  FOR  NURSES 

point  where  the  refracted  rays  meet  evenly  and  exactly, 
and  the  image  of  an  object  is  distinct,  is  exactly  on  the 


Fig.  74. — Detail  of  eye  (Butler,  "Household  Physics"). 


Fig-  75- — Accommodation  of  eye  for  distance:  a,  For  distant  ob- 
jects; b,  for  near  objects.     (Butler,  "Household  Physics.") 

retina.  The  muscles  of  accommodation,  acting  upon 
the  lens,  flatten  or  thicken  it,  and  change  the  focal 
point  as  objects  are  near  or  far  away. 


LIGHT 


153 


In  eyes  which  are  not  normal  the  focal  point  falls  too 
far  in  front  of  or  behind  the  retina,  and  the  image  formed 
there  is  blurred.  In  the  case  of  near-by  objects  we  may 


Fig.  76. — Correction  for  far-sighted  eye  by  glasses:    a,  Far-sighted 
eye;  b,  correction.     (Butler,  "Household  Physics.") 


Fig  77- — Correction  for  near-sighted  eye  by  glasses:  a,  Near-sighted 
eye;  b,  correction.     (Butler,  "Household  Physics.") 


154  PRACTICAL  PHYSICS  FOR  NURSES 

remedy  this  somewhat  by  changing  their  distance  from 
the  eye;  as  when  we  see  a  "far-sighted"  person  hold  a 
book  at  arm's  length  in  order  to  read  it  easily,  while  a 
"near-sighted"  person  holds  it  within  a  few  inches  of 
the  eye. 

Defects  in  the  structure  of  the  eye  may  be  congenital 
or  acquired.  They  are  overcome  by  the  use  of  glasses, 
which  are  lenses  of  shapes  varied  to  suit  the  needs  of 
the  particular  eye  in  question.  They  are  so  constructed 
as  to  bring  the  focal  point  exactly  on  the  retina.  Correct 
fitting  of  the  frames  or  mountings  is  also  important,  so 
that  the  focal  point  may  remain  in  its  proper  position. 


Fig.  78. — Head-mirror  (Morrow). 

OPTICAL  INSTRUMENTS 

The  head-mirror  used  by  physicians  has  a  concave 
reflecting  surface  designed  to  concentrate  light  in  order 


LIGHT  155 

to  throw  in  into  a  cavity,  thereby  illuminating  it.  The 
hole  at  the  center  enables  the  operator  to  see  the  spot 
upon  which  the  light  is  thrown,  while  the  dark  back  of 
the  mirror  shades  his  eyes  from  the  glare. 


Fig-  79- — Ophthalmoscopes. 

The  ophthalmoscope  is  similar  to  the  head-mirror. 
It  sends  into  the  interior  of  the  eyeball,  through  the 
pupil,  light  which  is  reflected  from  a  lamp  placed  back 
of  and  at  one  side  of  the  patient's  head.  The  rays  re- 


156  PRACTICAL  PHYSICS  FOR  NURSES 

fleeted  from  the  retina  through  the  pupil  come  back  to 
the  mirror,  through  the  hole  in  which  the  operator  may 
observe,  and  so  get  a  picture  of  the  interior  of  the  eye. 
The  laryngoscope  uses  a  concave  reflecting  mirror  or 
an  electric  light  to  throw  light  into  the  throat,  whence 
it  is  reflected  downward  by  a  flat  mirror  placed  at  such  an 


Fig.  80. — Laryngoscope  and  throat  mirrors. 

angle  that  it  will  throw  the  light  into  the  larynx.  This 
mirror  serves  the  double  purpose  of  a  reflector  for  the 
light  going  into  the  larynx  and  for  the  image  of  the  condi- 
tion existing  there  which  goes  back  to  the  observer's  eye. 
The  camera  is  an  artificial  eye.  It  has  a  double  convex 
lens  which  acts  exactly  as  does  the  lens  of  the  human  eye. 
The  accommodation,  or  change  for  objects  at  different 


LIGHT  157 

distances,  is  made  by  changing  the  position  of  the  lens 
itself.  Instead  of  the  retina  there  is  the  sensitized 
plate  or  film,  which  gives  us  a  permanent  record  of  the 
object. 

The  microscope  lens  refracts  the  rays  of  light  coming 
from  a  very  small  object,  so  that  the  lens  of  the  eye  can 


Fig.  81. — Image  in  the  compound  microscope  (Butler,  "Household 
Physics"). 


make  use  of  them.  As  the  eye  follows  those  rays  out, 
it  sees  the  object  larger  than  it  really  is.  The  compound 
microscope  has  a  double  set  of  lenses,  usually  five  or  more 


158  PRACTICAL  PHYSICS  FOR  NURSES 

in  all,  thereby  greatly  increasing  its  refraction  and  con- 
sequent magnifying  power. 


Fig.  82. — Telescope    (Butler,  "Household  Physics"). 

The  telescope  is  constructed  upon  principles  similar 
to  those  involved  in  the  microscope.  The  larger  tele- 
scopes make  use  of  reflection  as  well  as  refraction. 

COLOR 

A  prism  is  a  piece  of  glass  or  other  transparent  sub- 
stance having  two  of  its  sides  set  at  an  angle  to  each 
other.  It  may  be  used  to  refract  light  so  as  to  break 
it  up  into  its  component  parts. 

Experiment. — Pass  sunlight  through  a  glass  prism.     We  get 
a  band  of  rainbow-colored  light. 

By  this  means  we  discover  that  white  light  is  com- 
posed of  seven  "primary"  colors — violet,  indigo,  blue, 


LIGHT  159 

green,  yellow,  orange,  and  red.  Scientists  have  found 
that  the  red  rays  are  those  that  vibrate  most  slowly, 
while  the  violet  rays,  at  the  other  end  of  the  spectrum, 
vibrate  the  most  rapidly.  Correspondingly,  the  red 
waves  are  longest,  the  violet  waves  shortest.1 

The  Finsen  light  is  a  lamp  which  gives  out  ultra- 
violet rays,   that  is,  rays  which  vibrate  more  rapidly 


Fig.  83. — Prismatic  spectrum. 

than  even  the  violet  ones.  These  rays  produce  chemical 
changes  in  the  tissues  which  are  exposed  to  them. 

Color  is  the  impression  given  to  the  eye  by  light  of  varied 
rates  of  vibration. 

A  body  is  colored  when  it  reflects  only  a  portion  of  the 
white  light  that  comes  to  it -from  the  sun.  An  object 
or  substance  is  white  when  it  reflects  all  the  sunlight. 
It  appears  black  when  it  reflects  almost  no  light,  but, 
on  the  contrary,  absorbs  it. 

1  Red  waves  are  about  .0007  millimeter  in  length,  violet  waves 
about  .0004  millimeter. 


160  PRACTICAL  PHYSICS  FOR  NURSES 

Artificial  lights  have  different  wave  lengths  from 
sunlight  and  are  therefore  colored.  Their  color  mingles 
•with  that  reflected  from  objects  or  substances  which 
they  illuminate,  making  these  objects  appear  of  a 
different  color  from  what  they  do  in  daylight.  It  is 
for  this  reason  that  matching  of  colors  is  impossible 
except  in  daylight. 

SUMMARY 

Light  is  made  up  of  waves,  as  are  heat  and  sound. 
Light  waves  are  very  short  (about  aoooo  inch)  and 
travel  very  rapidly  (about  185,000  miles  per  second). 

Light  is  transmitted  by  the  ether,  a  material  which 
pervades  the  whole  universe. 

Light  travels  in  all  directions  from  its  source.  For 
convenience  we  refer  to  rays  of  light,  since  the  direction 
is  always  perfectly  straight. 

Light  waves  may  be  absorbed  by  a  substance  or  object, 
transmitted  by  it,  reflected,  or  refracted  by  it. 

When  light  is  stopped  by  an  opaque  body,  a  shadow 
is  produced  on  its  farther  side.  This  shadow  has  a 
sharp  edge  if  the  light  is  small,  blurred  if  it  is  large. 

We  see  only  objects  from  which  light  comes  to  us. 
They  may  be  luminous,  i.  e.,  giving  out  light,  or  they  may 
reflect  light  which  comes  to  them  from  another  source. 
Most  objects  are  seen  by  reflected  light. 

Light  is  reflected  in  the  opposite  direction  from  that 
of  its  approach,  and  at  exactly  the  same  angle.  If  it 


LIGHT  161 

comes  from  the  right,  it  is  reflected  to  the  left,  and  vice 
versa. 

Light  rays  may  be  refracted  or  bent  in  passing  from 
one  substance  to  another.  This  is  done  artificially  by 
means  of  lenses.  Convex  lenses  concentrate  light  rays, 
concave  lenses  distribute  them. 

A  focus  is  the  point  at  which  converging  rays  of  light 
come  together  and  produce  a  distinct,  clear-cut  image. 

Light  is  polarized  by  making  it  vibrate  in  one  direc- 
tion only,  in  parallel  rays.  The  direction  and  amount 
of  refraction  caused  by  a  substance  or  a  solution  which 
polarizes  light  may  be  used  as  a  test  for  determining  its 
presence. 

Light  enters  the  eye,  is  refracted  by  the  cornea,  passes 
through  the  pupil,  and  is  twice  refracted  and  concen- 
trated by  the  lens.  Normally  the  focal  point  is  exactly 
on  the  retina,  adjustment  for  near  or  far-away  objects 
being  made  by  the  ciliary  muscle.  The  pupil  regulates 
the  amount  of  light  which  enters  the  eye.  The  image 
formed  on  the  retina  is  transferred  to  the  brain  by  the 
optic  nerve. 

Eye  defects  may  be  overcome  by  means  of  glasses 
whose  lenses  change  the  focal  point  or  make  other 
needed  adjustments. 

The  various  optical  instruments  are  combinations  of 
lenses,  reflectors,  or  both.  They  may  reduce  or  magnify 
the  apparent  size  of  an  object,  illuminate  cavities,  and 
reflect  their  contents,  etc. 


162  PRACTICAL  PHYSICS  FOR  NURSES 

Sunlight  is  white  light.  It  may  be  broken  up  into  its 
seven  primary  colors.  Some  colors  are  formed  by  rapid 
vibrations,  some  by  slower  vibrations. 

An  object  appears  colored  when  it  reflects  only  part 
of  the  light  which  comes  to  it  from  the  sun.  Black 
objects  absorb  light  instead  of  reflecting  it;  white  ones 
reflect  all  the  light  coming  to  .them. 

Artificial  lights  are  themselves  colored,  therefore  they 
change  the  apparent  color  of  objects  which  they  illumi- 
nate. 


CHAPTER  XI 

ELECTRICITY 

What  We  Know  About  It. — Electricity  is  a  force  the 
nature  of  which  we  do  not  know.  We  know  how  to  pro- 
duce it,  how  to  control  it,  and  we  make  constant  use 
of  it;  but  no  one  has  been  able  to  define  it  nor  find  out 
what  it  is. 

Magnetism  is  a  species  of  electricity.  Magnetic 
iron  is  a  natural  product,  but  magnets  are  also  made 
artificially. 

Experiments. — Show  how  a  magnet  attracts  iron  filings,  tacks, 
etc.  Hold  it  outside  a  glass  of  water  containing  small  tacks;  it 
will  be  found  that  its  power  is  exerted  through  the  glass  and  through 
the  water. 

In  a  bar  magnet,  straight  or  curved,  it  is  found  that 
the  drawing  force  is  exerted  most  strongly  at  the  ends. 
These  are  called  the  poles. 


Fig.  84. — Iron  filings  clinging  to  pole  of  magnet  (Butler,  "Household 
Physics"). 

The  compass  needle  is  a  magnet  freely  suspended. 
One  end  of  such  a  magnet  will  always  be  found  seeking 

163 


164  PRACTICAL  PHYSICS  FOR  NURSES 

the  magnetic  pole  of  the  earth,  which  is  approximately 
north.  If  two  suspended  magnets  are  brought  near 
each  other,  the  north-seeking  ends  repel  each  other, 
but  a  north-  and  a  south-seeking  end  attract  each  other. 
Thus  we  find  that  the  poles  of  a  magnet  are  of  two  sorts, 
positive  and  negative.  We  also  find  that  unlike  poles 
attract  and  like  poles  repel  each  other. 


Fig.  85. — Mariner's  compass  (Butler,  "Household  Physics"). 

Electricity  may  be  produced  in  three  ways:  (1)  by 
friction,  (2)  by  chemical  action,  and  (3)  by  means  of  a 
dynamo.  We  recognize,  therefore,  three  varieties  of 
electricity,  yet  it  is  likely  that  they  are  merely  different 
manifestations  of  the  same  force. 

Frictional  Electricity. — Many  different  materials  pro- 
duce electricity  when  rubbed  briskly  under  favorable 
conditions.  In  dry,  cold  weather,  the  rubbing  of  the 
feet  on  a  carpet,  the  stroking  of  a  cat's  fur,  the  rubbing 
of  a  piece  of  hard  rubber  with  flannel,  or  a  glass  rod  with 
silk,  etc.,  produce  electricity.  One  can  often  see  the 


ELECTRICITY  165 

sparks  caused  by  its  discharge  or  escape.  When  fric- 
tional  electricity  is  produced  by  a  machine  it  is  done  by 
the  rapid  revolution  of  metal  brushes  against  glass 
plates;  the  electricity  so  produced  is  stored  in  Ley  den 
jars  and  is  allowed  to  escape  at  the  pleasure  of  the 
operator.  When  the  machine  is  in  motion,  a  prickling 


Fig.  86.— Holtz's  static  machine. 

sensation  (due  to  the  small  sparks  which  come  through 
the  air)  is  felt  by  a  person  standing  in  its  vicinity,  there 
is  a  peculiar  metallic  odor  due  to  the  chemical  effect,  the 
air  is  slightly  heated,  etc.  This  form  of  electricity  is 
called  static  (from  the  Greek  statikos,  brought  to  a  stand- 
still), because  it  may  be  stored. 


166  PRACTICAL  PHYSICS  FOR  NURSES 

Electricity  by  Chemical  Means. — In  producing  elec- 
tricity by  chemical  action  we  use  a  combination  of 
materials  which  we  call  a  cell.  Two  or  more  cells  con- 
nected are  termed  a  battery.1 

The  usual  "wet"  cell  is  composed  of  a  piece  of  zinc 
and  another  of  carbon  set  into  a  solution  of  sal  ammoniac, 
and  connected  at  their  dry  ends  by  a  wire,  usually  of 
copper.  The  chemical  action  of  the  solution  upon  the 


Fig.  87.— Wet  cell  (Butler,  "Household  Physics"). 

elements  (the  zinc  and  carbon)  starts  a  current,  which 
flows  through  the  wire.  The  carbon  is  the  negative 
element,  the  zinc  the  positive;  the  current  always  flows 
from  the  positive  to  the  negative. 

A  "dry"  cell  is  similar,  except  that  the  sal  ammoniac 
is  merely  damp  instead  of  being  wet,  the  moisture  being 
kept  in  by  a  tightly  sealed  container.  .  Dry  cells  do  not 
last  as  long  as  wet  ones,  and  are  more  expensive  in  pro- 
portion to  their  size,  but  require  less  attention. 

1  These  terms  are  often  confused. 


ELECTRICITY  167 

The  wires  connected  with  the  elements  of  a  cell  com- 
plete what  is  called  the  electrical  circuit.  When  the 
wire  is  continuous,  the  circuit  is  closed,  and  the  current 
flows.  When  the  wire  is  broken,  cut,  or  removed,  the 
circuit  is  open,  and  the  current  stops. 

(It  is  possible,  however,  for  electric  current  to  leap 
across  a  short  break  in  the  circuit,  producing  a  spark.) 

In  the  wiring  for  electric  lights,  the  switch  or  button 
makes  the  connection  between  the  two  open  ends  of 


Fig.  88.— Dry  cell  (Butler,  "Household  Physics"). 

the  circuit  and  allows  the  current  to  flow.  The  light 
burns  so  long  as  the  connection  is  maintained.  When 
the  circuit  is  broken  by  turning  the  button  or  switch, 
the  light  goes  out  because  of  the  interruption  of  the 
current. 

Electricity  by  Dynamo. — If  a  coil  of  wire  be  moved  in 
the  immediate  vicinity  of  a  magnet,  a  current  of  elec- 
tricity is  set  up  in  the  wire.  A  machine  which  thus 
converts  motion  into  electric  energy  is  called  a  dynamo. 


168  PRACTICAL  PHYSICS  FOR  NURSES 

Its  essential  parts  are  the  rotating  coil  or  armature,  and 
the  large  magnet,  called  the  field  magnet. 

Motors. — Conversely,  machines  have  been  made  which 
will  convert  electric  energy  into  motion.  Such  machines 
are  called  motors. 


Fig.  89.— Electric  motor  (Tousey). 

Electric  Heating. — When  a  strong  electric  current  is 
passed  through  a  wire  which  is  too  small  to  carry  it  properly, 
the  wire  becomes  heated.1  Wires  large  enough  to  carry 
the  current  do  not  become  hot. 

Electric  heaters  are  made  with  fine  wires,  which  are 
also  of  a  material  which  does  not  conduct  electricity 
well;  these  resist  the  passage  of  the  current  and  so  be- 
come heated.  The  electric  flat-iron,  the  electric  toaster, 
electric  stove,  electric  heating  pad,  etc.,  have  their 

1  This  may  be  the  cause  of  some  of  the  fires  due  to  "defective 
wiring." 


ELECTRICITY  169 

"heating  elements"  made  of  fine  wire  surrounded  by  or 
embedded  in  some  substance  which  insulates  it  from  the 


a  b 

Fig.  90. — Wiring  in  electric  flatiron:     a,  Electric  flatiron;  b,  wire 
grid.     (Butler,  "Household  Physics.") 

surrounding  objects,  but  permits  the  heat  to  be  given 
off  in  any  desired  direction.    The  electric  cautery  is 


Fig.  91. — Incandescent  electric  lamp  (Butler,  "Household  Physics"). 

constructed  upon  the  same  principles;  its  advantage  is 
that  the  degree  of  heat  can  be  controlled,  so  that  a  high 


1 70  PRACTICAL  PHYSICS  FOR  NURSES 

or  low  temperature  may  be  employed.  (This  is  done  by 
means  of  special  apparatus.) 

If  from  any  cause  these  appliances  get  too  hot,  they 
"burn  out,"  i.  e.,  the  wire  is  destroyed  and  must  be  re- 
placed before  they  can  be  used. 

Electric  Lights. — If  a  finer  wire  or  a  stronger  current 
is  used  than  is  employed  in  heating  apparatus,  the  wire 
may  become  white  hot,  so  that  it  gives  out  light.  This 
is  the  principle  underlying  the  incandescent  electric 
bulb,  in  which  a  strong  current  is  passed  through  a  very 
fine  filament.  The  thin  glass  which  encloses  it  has  had 
the  air  pumped  out  of  it  and  is  sealed  tightly,  so  that  no 
oxygen  can  get  in  to  support  combustion  and  cause  the 
filament  to  burn  up. 

The  arc  light  is  made  with  two  sticks  of  carbon,  a 
substance  which  melts  or  burns  up  with  difficulty. 
These  sticks  are  arranged  so  that  the  current  has  to 
leap  across  a  small  space  between  them;  in  so  doing,  it 
heats  them  white  hot,  producing  a  brilliant  light. 

The  fuse  in  an  electric  lighting  system  is  a  bit  of  metal 
which  fuses  or  melts  at  a  low  temperature.  If  for  any 
reason  the  current  becomes  too  strong,  the  fuse  by 
melting  breaks  the  connection;  in  this  way  the  lighting 
system  is  protected  against  sudden  increase  of  current 
from  trouble  at  the  power-house,  influence  of  electric 
storms,  etc.  Telephones  have  similar  arrangements  at 
the  central  station;  when  these  fuses  burn  out  (melt) 
because  of  wires  being  struck  by  lightning,  or  from  any 


ELECTRICITY 


171 


other  cause,  they  can  readily  be  renewed  and  the  con- 
nection re-established. 

Electromagnet. — If  a  bar  of  soft  iron  be  wound  with 
wire  and  an  electric  current  passed  through  the  wire,  the 


Mains.   Switch, 


Fig.  92. — i,  Fuses  and  their  action:  a,  Link  fuse;  b,  screw  in- 
closed fuse  and  base;  c,  cartridge  fuse  and  base;  d,  cartridge  fuse 
cut  open,  exposing  fuse  metal.  2,  Lamps  in  house  grouped  in  paral- 
lel. (Butler,  "Household  Physics.") 

iron  becomes  a  magnet.  It  remains  magnetized  so 
long  as  the  current  flows.  This  is  called  an  electro- 
magnet. 


172 


PRACTICAL  PHYSICS  FOR  NURSES 


An  electromagnet  is  much  stronger  than  any  other 
sort  of  magnet.  Its  power  depends  upon  the  strength 
of  the  current  flowing  through  the  wire  and  upon  the 
number  of  turns  of  wire.  Examine  the  coil  in  an  elec 
trie  machine  and  you  will  find  that  there  are  a  vast 
number  of  turns  of  very  fine  wire. 

The  eye  magnet,  used  to  extract  pieces  of  metal  from 
the  eye  or  other  portions  of  the  body,  is  a  strong  electro- 


Fig.  93. — a,  Straight  bar  electromagnet;  b,  horseshoe  electromagnet. 
(Butler,  "Household  Physics.") 

magnet.  If  large  enough,  it  will  pull  out  a  needle  which 
is  embedded  \  inch  in  the  flesh. 

The  so-called  "vibreur,"  or  electromagnetic  vibrator, 
is  used  to  locate  metallic  foreign  bodies.  They  are  first 
located  approximately  by  means  of  the  #-ray;  then, 
if  not  too  deeply  embedded,  they  are  found  with  great 
accuracy  by  applying  the  vibrating  magnet.  The  pa- 
tient's sensations  aid  in  the  operation. 

In  the  electric  telegraph  an  electromagnet  pulls  down 


ELECTRICITY 


173 


an  iron  lever;  this  makes  a  mark  upon  or  a  puncture  in  a 
moving  paper  ribbon,  the  result  being  a  dot  or  a  dash, 
according  to  the  length  of  time  that  the  lever  is  held 
down.  The  operator  makes  and  breaks  the  circuit  which 
induces  the  power  in  the  magnet,  thus  producing  a  series 
of  dots,  dashes,  and  spaces;  these  constitute  the  Morse 
alphabet. 


Insulator 


fed 


Fig.  94. — Telephone  receiver  and  transmitter  (Butler,  "Household 
Physics"). 

In  the  telephone  the  voice  striking  against  a  thin 
iron  disk  sets  it  vibrating.  These  vibrations  make  and 
break  the  current  induced  in  an  electromagnet  which  is 
in  the  receiver.  The  wire  transmits  the  vibrations  in 
all  their  peculiar  quality,  and  a  similar  instrument 
at  the  other  end  reproduces  them. 

In  the  electric  bell  the  push  of  the  button  makes  the 
connection  between  twro  ends  of  wire  which  complete 
the  circuit.  When  the  circuit  is  closed,  current  passes 


174  PRACTICAL  PHYSICS  FOR  NURSES 

through  a  small  electromagnet  which  pulls  the  clapper 
back,  making  it  strike  the  bell.  There  is  in  the  mechan- 
ism an  arrangement  for  a  rapid  making  and  breaking 
of  the  circuit,  producing  the  intermittent,  buzzing  ring. 
When  an  electric  bell  does  not  work,  one  of  several 
things  may  be  the  difficulty.  Nearly  all  of  them  may 
be  remedied  by  very  simple  measures.  A  new  dry  cell 


Fig-  95- — Electric  bell  (Butler,  "Household  Physics"). 

may  be  needed  for  the  battery;  more  water  or  fresh 
solution,  if  it  is  a  wet  cell.  The  commonest  trouble  oc- 
curs at  the  push-button,  where  the  connection  may  fail 
to  be  made  because  a  wire  has  slipped  or  been  worn 
through.  Frayed  ends  of  wire  cause  the  current  to  be 
conducted  to  other  things  and  so  be  useless.  Accumula- 
tion of  dust  on  the  electromagnet  may  prevent  its  work- 
ing properly.  Only  very  occasionally  is  there  trouble 
in  the  wire  itself. 


ELECTRICITY  175 

If  a  bell  rings  continuously,  the  difficulty  is  usually 
in  the  push-button,  or  possibly  in  the  wires.  A  simple 
inspection  of  the  interior  of  the  button  reveals  the  trouble 
in  most  cases,  and  it  is  quickly  remedied.  The  mere 
stopping  of  the  sound  of  the  bell  (by  pushing  something 
between  it  and  the  clapper)  is  not  advisable,  since  in 
this  case  the  battery  or  cell  "runs  down,"  i.  e.,  is  worn 
out,  very  rapidly. 

Rate  of  Speed. — Electricity  travels  at  the  same  rate 
of  speed  that  light  does,  185,000  miles  per  second. 

Electric  Measures. — A  volt  is  the  measure  of  electric 
pressure  or  force. 

An  ohm  is  the  measure  of  electric  resistance. 

An  ampere  is  the  measure  of  electric  current. 

When  a  force  of  1  volt  overcomes  a  resistance  of  1 
ohm,  a  current  of  1  ampere  results. 

A  watt  is  the  measure  of  amount  of  electricity. 

Conductors  of  Electricity. — Some  substance  are  good 
conductors  of  electricity,  other  are  not.  Cotton,  linen, 
water,  the  human  body,  etc.,  are  neutral,  being  neither 
very  good  nor  very  poor.  The  most  satisfactory  con- 
ductor of  electricity  and  the  one  in  most  common  use  is 
copper  wire.  Most  metals  are  good  conductors,  though 
they  vary  in  degree.  Acids  are  likewise  good. 

Poor  conductors  of  electricity  are  called  insulators. 
They  are  used  to  interrupt  or  ward  off  electric  current. 
Such  substances  are  hard  rubber,  glass,  wood,  etc. 

Electric  Treatments. — Electricity  is  used  in  the  treat- 


176  PRACTICAL  PHYSICS  FOR  NURSES 

ment  of  disease,  usually  in  order  to  stimulate  some  por- 
tion of  the  body  to  a  proper  performance  of  its  function, 
or  to  help  the  process  of  nutrition  or  metabolism. 

Static  electricity  is  produced  in  the  so-called  static 
machine  (see  page  165)  by  friction.  It  is  used  to  reg- 
ulate functional  processes,  circulation,  secretion,  nu- 
trition, etc.  It  is  also  of  value  in  some  inflammatory 
conditions  and  paralyses. 

Galvanic  electricity  is  produced  by  a  cell  or  battery, 
and  gives  a  vibration.  It  is  used  in  the  diagnosis  and 
treatment  of  nervous  disorders  and  in  some  forms  of 
paralysis. 


Fig.  96. — Induction  coil. 

Faradic  electricity  is  produced  by  an  induction  coil, 
and  is  felt  as  vibration.  It  is  used  as  a  tonic,  is  em- 
ployed in  rheumatism,  in  eczema,  and  in  nervous  con- 
ditions, etc. 

High-frequency  current  is  used  to  promote  elimina- 
tion, reduce  blood-pressure,  relieve  pain,  etc. 


ELECTRICITY  177 

SUMMARY 

Electricity  is  a  force  the  nature  of  which  we  do  not 
know,  though  we  use  it  commonly,  can  produce  and 
control  it. 

Magnetism,  a  species  of  electricity,  occurs  in  nature 
or  may  be  produced  artificially.  The  mariner's  compass 
has  a  magnetic  needle  one  of  whose  ends  or  poles  always 
seeks  the  north. 

Electricity  may  be  produced  by  friction,  by  chemical 
action,  or  by  a  dynamo. 

Many  different  materials  may  be  used  to  make  fric- 
tional  electricity.  In  the  static  machine  it  is  produced 
by  revolving  metal  brushes  against  plates  of  glass,  and 
is  stored  in  Leyden  jars. 

Electricity  is  produced  through  chemical  action  by 
means  of  certain  combinations  of  materials  called  a  cell. 
The  essential  parts  of  a  cell  are  its  two  elements  (usually 
metals),  the  solution,  and  the  connecting  wire.  When 
complete,  it  forms  an  electric  circuit,  through  which 
a  current  flows.  This  circuit  may  be  closed  or  opened 
(made  or  broken)  at  will  by  means  of  a  switch  or  other 
device.  When  electricity  leaps  across  a  break  in  a 
circuit,  it  produces  a  spark. 

The  essential  parts  of  a  dynamo  are  the  field  magnet 
and  the  armature  (a  rotating  coil  of  wire).  The  magnet 
induces  an  electric  current  in  the  wire. 

Motors  are  machines  which  convert  electric  energy 
into  motion. 


178  PRACTICAL  PHYSICS  FOR  NURSES 

When  an  electric  current  is  forced  through  a  wire  too 
small  to  carry  it,  heat  is  produced.  The  various  elec- 
tric appliances  in  domestic  and  hospital  use  are  con- 
structed in  accordance  with  this  law. 

Electric  lighting  comes  under  the  same  law.  A  still 
smaller  wire  is  used,  or  some  substance,  as  carbon, 
which  fuses  with  great  difficulty.  The  filaments  of 
incandescent  lights  are  enclosed  in  vacuum  globes  so 
as  to  cut  off  oxygen  and  so  prevent  their  combustion. 

A  fuse  is  a  piece  of  metal  which  melts  at  a  low  tem- 
perature. It  is  used  to  protect  electric  light  or  tele- 
phone systems  from  a  sudden  increase  of  current  which 
would  cause  them  to  burn  out. 

An  electromagnet  is  a  bar  of  soft  iron  wound  with 
wire  through  which  an  electric  current  is  passed;  the 
iron  becomes  strongly  magnetized.  The  electromagnet 
is  a  vital  part  of  the  mechanism  of  the  telegraph,  tele- 
phone, electric  bell,  etc. 

When  an  electric  bell  does  not  work,  it  is  usually  due 
to  some  simple  trouble  which  can  be  revealed  by  in- 
spection and  easily  remedied. 

Electricity  travels  at  the  rate  of  185,000  miles  per 
second. 

The  volt,  the  ohm,  the  ampere,  and  the  watt  are 
electric  measures. 

Metals,  acids,  etc.,  are  good  conductors  of  electricity. 
Wood,  glass,  rubber,  etc.,  are  poor  conductors,  and  are 
used  to  insulate  against  electricity.  The  human  body 


ELECTRICITY  179 

is  neutral,  neither  good  nor  bad,  as  a  conductor  of  elec- 
tricity. 

Static  electricity  (frictional),  galvanic  electricity 
(chemical),  faradic  electricity  (from  an  induction  coil), 
and  the  high-frequency  current  are  used  in  medical 
treatment. 


CHAPTER  XII 

THE  x-RAY.     RADIUM 

THE  ROENTGEN  OR  x-RAYS 

History  of  the  JC-Ray. — It  has  long  been  known  that  an 
electric  spark  would  pass  more  readily,  leap  farther, 
through  rarefied  air  than  through  ordinary  air.  Late 
in  the  nineteenth  century  Sir  William  Crookes  worked 
out  a  special  vacuum  tube,  in  which  the  air  was  so  rare- 
fied that  there  was  but  one-millionth  as  much  as  in  a 


Fig-  97- — A  Crookes  tube,  showing  reflected  "x-rays." 

corresponding  space  in  the  atmosphere.  He  connected 
this  "high"  vacuum  tube  between  the  terminals  or  poles 
of  a  machine  that  produced  the  correct  sort  of  electric 
current.  It  was  so  arranged  that  the  discharge  or 
spark  took  place  between  the  two  electrodes  (metal  con- 
ductors which  introduce  and  withdraw  the  current)  in 
the  tube.1 

1  In  the  Crookes  tube  of  high  vacuum  the  electric  force  causes 
the  glass  of  the  tube  to  become  phosphorescent. 
180 


THE  z-RAY.     RADIUM  181 

It  was  found  that  in  the  Crookes  tube  connected  with 
an  electric  machine  which  was  set  in  motion  something 
radiated  in  straight  lines  from  the  negative  electrode  or 
terminal.  This  something  was  named  the  cathode  ray. 
Later  Conrad  Roentgen  found  that  if  the  cathode  rays 
were  reflected  from  the  walls  of  the  tube  or  from  a 
special  reflector  or  obstacle  placed  in  the  tube,  a  new  sort 
of  rays  with  special  powers  were  produced.  These  he 
named  z-rays,  x  in  algebra  signifying  an  unknown 
quantity.  They  are  also  called  Roentgen  rays. 

Characteristics  of  the  *-Ray. — We  know  very  little 
of  the  nature  of  #-rays,  but  we  make  use  of  them  in  some 
very  definite  ways. 

They  act  upon  a  photographic  plate  exactly  as  daylight 
does  (the  action  is  chemical),  and  produce  a  picture  of 
whatever  is  in  front  of  the  plate. 

So  far  as  we  know,  #-rays  cannot  be  reflected  nor  re- 
fracted, nor  in  other  ways  manipulated  as  light  rays  are. 
They  have  very  little  effect  upon  the  human  eye. 

At  present  we  know  of  no  means  of  bringing  x-rays 
to  a  focus;  photographs  taken  by  their  means  must 
always  be  close  to  the  object  and,  therefore,  life  size. 

The  most  striking  characteristic  of  the  z-ray  is  that 
it  passes  through  substances  which  light  will  not  pene- 
trate, such  as  wood,  clothing,  cardboard,  flesh,  etc. 
Most  metals  stop  it,  aluminum  being  the  chief  excep- 
tion. Surgical  dressings  of  gauze  and  cotton  do  not 
interfere  with  the  passage  of  the  #-ray;  but  iodoform, 


182 


PRACTICAL  PHYSICS  FOR  NURSES 


plaster  casts,  adhesive  plaster,  and  wood  splints  are  said 
to  cast  shadows.  If  there  is  a  metallic  foreign  body  to 
be  located,  these  things  do  not  interfere  materially  with 
the  process;  but  if  the  soft  tissues  are  to  be  carefully 


Fig.  98.— x-Ray  of  intestine  (Gant). 

examined,  it  is  wisest  to  remove  any  of  the  above  dress- 
ing materials. 
Bismuth  is  quite  opaque  under  the  x-ray.    Taken 


THE  *-RAY.    RADIUM  183 

internally,  bismuth  coats  the  stomach  and  intestines, 
making  it  possible  to  see  very  clearly  their  outlines  under 
the  x-ray.  Bismuth  "meals"  or  enemata  are,  therefore, 
used  to  aid  in  the  diagnosis  of  conditions  existing  in  the 
alimentary  canal. 

The  Fluoroscope. — It  was  found  that  certain  sub- 
stances, fluorescent  materials,  such  as  calcium  tungstate, 
barium  cyanid,  etc.,  become  luminous  under  the  x-ray. 


Fig.  99- — Fluoroscope. 

The  fluoroscope  was,  therefore,  constructed  so  that  the 
#-ray  shadow  picture  falls  on  a  screen  of  fluorescent 
material,  which  illuminates  it,  causing  it  to  be  distinctly 
seen.  It  is  used  in  making  x-ray  examinations. 

Uses  of  the  x-Ray. — The  x-ray  is  used  in  medicine  and 
surgery  to 

(1)  Locate  foreign  bodies. 

(2)  Locate  fractures  of  the  bones. 

(3)  Discover  diseased  conditions.    These  can  be  seen 
when  the  tissue  change  involved  is  considerable. 


1 84  PRACTICAL  PHYSICS  FOR  NURSES 

(4)  In  stomach  and  intestinal  work,  to  discover  dis- 
placements,   strictures,   ulcers,   etc.,   and    to   note    the 
rapidity  of  functional  processes. 

(5)  Produce  permanent  photographs  of  the  findings. 

(6)  The  #-ray  has  been  used  with  some  success  in  the 
treatment  of  lupus,  exophthalmic  goiter,  ulcers,  etc. 

x-Ray  Burns. — For  some  years  after  the  x-ray  came 
into  use  it  was  found  that  too  long  or  too  frequent 


Fig.  IOO. — ;c-Ray  of  fractured  fibula  (Scudder). 

exposure  to  it  produced  burns1  which  were  very  difficult 
to  heal,  and  which  were  followed  in  some  cases  by 
cancer  or  some  malignant  growth. 

Protection  against  such  burns  is  now  had  by  the  use 
of  sheets  of  lead  as  screens,  by  rubber  gloves  contain- 
ing lead,  by  lead  glass  (glass  into  which  lead  is  incor- 

1  It  is  now  also  believed  that  the  burns  were  sometimes  due  to 
tubes  in  which  the  vacuum  was  poor, 


THE  *-RAY.    RADIUM  185 

porated),  etc.    In  consequence,  these  burns  are  now  very 
rare. 

RADIUM 

History  and  Characteristics. — Radium  is  a  very 
mysterious  substance,  with  some  remarkable  properties. 
It  was  discovered  and  isolated  in  1898  by  Madame  Curie 
of  France. 

Radium  is  one  of  a  group  of  substances  (uranium, 
helium,  etc.)  which  give  out  energy  at  a  very  rapid  rate. 
They  also  emit  rays,  which  affect  a  photographic  plate, 
produce  phosphorescence,  discharge  electrified  bodies, 
and  traverse  bodies  that  are  opaque  to  ordinary  light. 
Shenstone,  in  "The  New  Physics,"  sums  it  up  as  fol- 
lows: "Radium  gives  off  plentifully  certain  radiations 
which  exhibit  wonderful  powers  of  generating  light 
and  heat,  renders  various  minerals  phosphorescent,  and 
causes  the  air  to  conduct  electricity.  It  also  emits  an 
emanation. 

"It  does  these  things  for  long  periods,  without  any 
perceptible  diminution  of  its  powers,  and  will,  it  is  cal- 
culated, continue  to  do  them  for  thousands  of  years 
before  it  is  exhausted." 

Theories  in  Regard  to  Radium. — Nearly  one  hundred 
years  ago  Faraday  classified  matter  into  four  groups, 
instead  of  the  usual  three.  He  called  these  groups  solid, 
liquid,  gaseous,  and  radiant  matter.  He  held  that 
while  in  solids  the  molecules  were  held  firmly  in  place 
by  cohesion,  in  liquids  less  firmly,  and  while  in  gases 


1 86  PRACTICAL  PHYSICS  FOR  NURSES 

they  were  struggling  gently  to  get  away  from  each  other, 
in  radiant  matter  they  were  fleeing  from  one  another  with 
great  force. 

The  present  theory  is  that  the  atoms  of  a  "radio- 
active" substance  are  continually  subject  to  a  dis- 
integration (breaking  up)  that  takes  place  violently, 
throwing  off  particles  which  constitute  the  "emanation," 
i.  e.,  radium  gas.  The  wreck  of  the  old  atom  gives  rise 
to  a  new  atom,  which  may,  in  turn,  go  through  a  similar 
disintegration.  The  process  goes  on  till  only  stable 
atoms  are  formed. 

It  is  estimated  that  radium  disintegrates  one-half  in 
two  thousand  years. 

Radium  compounds,  or  "salts,"  also  apparently 
undergo  a  spontaneous  and  continuous  disintegration, 
or  tearing  apart.  In  this  rapid  and  violent  disintegration 
energy  is  released  to  a  remarkable  degree.  It  amounts 
to  100,000  times  as  much  energy  as  is  given  off  in  any 
known  chemical  change.  There  is  doubtless  a  limit  to 
this  radio-activity,  but  it  has  not  yet  been  found. 

Radium  compounds  are  found  to  be  always  two  de- 
grees hotter  than  their  surroundings,  a  fact  suggestive 
but  unexplained. 

Production  of  Light  and  Heat. — Radium  and  all  its 
compounds  evolve  heat  and  light.  Radium  itself  is  lu- 
minous. It  burns  the  skin  when  exposed  for  any  length 
of  time,  or  when  exposed  frequently  for  short  periods. 
Those  who  work  with  radium  invariably  have  the 


THE  x-RAY.    RADIUM  187 

papillae  of  the  skin  of  their  finger-ends  burnt  off,  the 
nails  cracked  and  split,  etc.  Whether  this  is  harmful 
or  not  has  not  been  determined. 

Radium  Rays. — There  are  three  distinct  kinds  of 
rays  given  off  by  radium:  the  alpha  (a),  beta  (/3),  and 
gamma  (r)  rays.  The  alpha  rays  can  be  stopped  by  a 
sheet  of  paper;  the  beta  rays  penetrate  thin  aluminum; 
the  gamma  rays  affect  a  photographic  plate  as  #-rays  do, 
and  can  be  stopped  only  by  thick  plates  of  lead.  The 
beta  and  gamma  rays  penetrate  the  tissues  of  the 
human  body. 

Uses  of  Radium. — Treatment  of  disease  with  radium 
is  still  in  the  experimental  stage.  It  is  being  used  with 
apparent  success  in  cancer  (epithelioma,  sarcoma,  and 
carcinoma),  in  exophthalmic  goiter,  in  removing  keloid, 
and  some  sorts  of  scar,  etc.  It  is  used  both  internally 
and  externally. 

Only  a  minute  quantity  is  needed  to  produce  a  marked 
effect. 

Radium  emanation  (the  gas)  is  also  used  in  treatment. 
It  is  given  off  from  both  radium  and  the  compounds. 
This  gas  remains  radio-active  for  about  four  days,  then 
disintegrates  and  loses  its  power.  The  so-called  radium 
waters  or  solutions  are,  for  this  reason,  usually  inef- 
fective. 

The  whole  amount  of  radium  in  the  world  at  the 
present  time  is  but  a  few  ounces,  but  its  remarkable 
energy  makes  this  in  effect  a  very  large  quantity. 


1 88  PRACTICAL  PHYSICS  FOR  NURSES 

SUMMARY 

The  x-ray  is  produced  by  the  discharge  of  an  electric 
current  in  a  special  sort  of  vacuum  tube. 

It  penetrates  many  materials  which  are  opaque  to 
light,  such  as  flesh,  clothing,  surgical  dressings,  etc., 
and  to  a  lesser  degree  wood,  plaster  casts,  and  adhesive 
plaster,  etc.  It  cannot  be  refracted  nor  brought  to  a 
focus.  It  does  not  impress  the  human  eye,  but  acts 
upon  a  photographic  plate  as  light  does. 

The  #-ray  is  used  in  locating  foreign  matter  in  the 
human  body,  or  fractures  of  bones,  in  discovering  diseased 
conditions,  organic  displacements,  etc.  Photographs  of 
the  conditions  found  are  taken  by  means  of  it. 

It  has  been  used  with  some  success  in  the  treatment 
of  external  troubles. 

The  fluoroscope  is  a  screen  of  some  material  which 
becomes  luminous  under  the  #-ray.  It  is  used  in  mak- 
ing examinations. 

#-Ray  burns,  due  to  long  or  frequent  exposures,  were 
formerly  common  and  dangerous.  They  are  now  pre- 
vented by  screens  of  lead  or  lead  glass. 

Radium  is  a  mysterious  substance,  similar  to  uranium 
and  helium,  which  is  radio-active,  i.  e.,  generates  heat 
and  light,  causes  phosphorescence,  emits  rays  similar 
to  the  #-ray,  etc.  It  was  discovered  in  1898  by  Madame 
Curie. 

It  is  thought  that  the  atoms  of  radium  are  constantly 
and  violently  disintegrating,  thus  releasing  an  enormous 


THE  s-RAY.    RADIUM  189 

amount  of  energy.  Its  compounds  and  gas  are  similar 
in  action  to  the  element  itself. 

Three  sorts  of  rays  are  given  off  by  radium,  the  alpha 
rays  being  feeble,  the  beta  and  gamma  more  active. 
The  two  latter  penetrate  the  human  body  and  cause 
tissue  changes  therein.  The  gamma  rays  affect  a  pho- 
tographic plate. 

Radium  and  its  compounds  are  being  used  with  ap- 
parent success  in  the  treatment  of  cancer  and  some  ex- 
ternal conditions. 

Radium  emanation  (the  gas)  remains  active  only  a 
comparatively  short  time. 

There  are  but  a  few  ounces  of  manufactured  radium 
in  the  world  at  the  present  time. 


CHAPTER  XIII 

QUESTIONS  FOR  REVIEW  OF  PRINCIPLES  AND 
ORIGINAL  THINKING 

1.  ARE  the  following  substances  organic  or  inorganic? 
Coal,  wood,  tile,  marble,  cork,  a    tumbler,  absorbent 
cotton,  gauze,  drainage-tubing,  cement  flooring,  baking 
powder,  salt,  corn  flour,  acetanilid,  tincture  of  digitalis, 
castor  oil,   antidiphtheric   serum,   bismuth   subnitrate, 
ichthyol,  bichlorid  of  mercury. 

2.  Are  the  following  physical  or  chemical  processes? 
Rising  of  cream,  rising  of  bread,  making  salt  solution, 
toasting    bread,    melting    butter,    freezing    ice-cream, 
ringing  an  electric  bell,  purging  by  castor  oil,  sterilizing 
instruments,  disinfection  of  linen  by  carbolic  solution, 
production  of  the  rainbow,  making  x-ray  pictures. 

3.  Why  does  an  automobile  skid  when   turning  a 
corner? 

4.  Why  is  a  passenger  thrown  backward  or  forward 
when  a  car  suddenly  starts  or  stops? 

5.  Why  is  dancing  easier  than  walking? 

6.  Why  does  stamping  remove   snow  or  mud   from 
one's  shoes? 

7.  Why  does  beating  remove  dust  from  a  rug? 

8.  Why  do  rubber  heels  make  walking  more   com- 
fortable? 

190 


QUESTIONS  FOR  REVIEW  191 

9.  Why  is  the  arch  of  the  foot  an  advantage? 

10.  What    is    a    crystalloid    substance?     A    colloid 
substance? 

11.  Why  is  it  harder  to  carry  a  load  upstairs  than  on 
a  level? 

12.  Why  can  a  person  crawl  over  thin  ice  when  it 
would  give  way  were  he  walking? 

13.  Why  is  it  dangerous  to  stand  up  in  a  small  boat? 

14.  Why  are  ink  bottles  made  with  thick  bottoms? 

15.  Upon  what  principle   is   the  laundry  extractor 
made? 

16.  Why  must  sewing  machines  be  frequently  oiled? 

17.  Why  do  we  put  sand  on  icy  sidewalks? 

18.  Why  do  knots  stay  tied? 

19.  How  do  chains  prevent  a  motor  car  from  skidding? 

20.  Why   can   a   heavy  piece   of   furniture   be   best 
moved  by  pushing  low  down  on  it? 

21.  What  sort  of  a  machine  is  the  coffee  mill?     The 
claw    of    a    hammer?     Grass    clippers?     A    retractor? 
A  nasal  speculum?    A  needle?    A  curling  iron?    A  door 
knob? 

22.  Why  does  cream  rise? 

23.  Explain  the  use  of  a  life-preserver. 

24.  Why  do  we  hang  the  container  high  in  giving 
hypodermoclysis?    Why  low  in  giving  a  Murphy  drip? 

25.  Explain  the  action  of  a  blotter,  or  of  absorbent 
cotton. 

26.  Why  is  a  new  towel  inefficient  for  drying  purposes? 


1 92  PRACTICAL  PHYSICS  FOR  NURSES 

27.  Discuss  the  drainage  of  wounds  from  the  stand- 
point of  physics. 

28.  Why  does  paint  or  varnish  preserve  wood? 

29.  Why  do  we  wear  rubbers? 

30.  What  happens  when  one  of  the  valves  of  the  heart 
fails  to  act? 

31.  What  is  a  trap  in  plumbing? 

32.  What  would  you  do  if  a  kitchen  "boiler"  leaked? 
A  hot-water  pipe?    A  cold-water  pipe? 

33.  What  happens  when  the  chest  wall  is  punctured, 
an  opening  made  through  into  the  lung? 

34.  How  does  a  pneumatic  door-check  work? 

35.  Explain  how  a  medicine-dropper  works? 

36.  Explain  the  draft  in  a  chimney. 

37.  Why  does  a  fireplace  ventilate  a  room? 

38.  Why  do  we  place  the  ice  in  the  top  of  a  refrigerator 
rather  than  the  bottom? 

39.  Why  does  a  furnace  sometimes  fail  to  heat  a 
certain  room? 

40.  Why  do  stoves  sometimes  smoke  when  a  fire  is 
first  started? 

41.  What  is  the  best  way  to  air  a  room?    Why? 

42.  Why  can  a  room  be  aired  more  quickly  in  winter 
than  in  summer? 

43.  Why  are  heaters  always  placed  in  the  basement? 

44.  Why  may  one  sometimes  be  more  comfortable  on 
a  day  when  the  thermometer  stands  at  90  degrees,  than 
on  a  day  when  it  is  82  degrees? 


QUESTIONS  FOR  REVIEW  193 

45.  How  can  you  loosen  a  glass  stopper  which  sticks? 
Why? 

46.  Why  is  water  not  used  in  a  thermometer? 

47.  Why  is  the  bulb  of  a  clinical  thermometer  made 
so  long?     Why  is  the  bore  made  so  small? 

48.  Why  are  the  grates  of  stoves  and  furnaces  fitted 
loosely  and  not  fastened? 

49.  Why  do  water  pipes  burst  when  they  freeze? 

50.  Why  is  the  amount  of  ice-cream  produced  by  a. 
freezer  greater  than  the  amount  of  liquid  put  in? 

51.  Why  does  a  lamp  chimney  crack  when  a  drop  of 
water  falls  on  it? 

52.  Why  are  thin  tumblers  less  likely  to  crack  than 
thick  ones  when  placed  in  hot  water? 

53.  Why  is  a  cotton  comfortable  warmer  than  a  wool 
blanket? 

54.  Why  is  a  vacuum  bottle  silvered? 

55.  Why  does  bread  or  cake  rise  when  being  baked? 

56.  Of  what  advantage  is  the  fireless  cooker? 

57.  Why  are  stone  houses  cooler  than  wooden  ones  in 
summer? 

58.  Why  are  heating  pipes  or  steam  pipes  sometimes 
covered  with  asbestos  or  felt? 

59.  How  does  a  tea-cosy  keep  the  tea  warm? 

60.  Why  does  a  hot-water  bag  remain  warm  so  long? 

61.  Why   are   soapstones   used   in   a   fireless   cooker 
rather  than  plates  of  iron? 

62.  Why  do  we  cover  an  ice-cream  freezer  with  a 

13 


194  PRACTICAL  PHYSICS  FOR  NURSES 

blanket  after  the  freezing  has  been  accomplished?    Why 
do  we  not  empty  the  melted  ice  from  around  the  can? 

63.  Why  is  a  wooden  tub  better  than  a  metal  one  for 
the  outside  of  a  freezer? 

64.  Why  should  we  not  wrap  the  ice  that  is  put  into 
a  refrigerator? 

65.  Why  is  ice  better  than  ice  water  for  cooling  a 
refrigerator? 

66.  Why  must  a  laundry  dry  room  have  a  fan  in  order 
to  do  rapid  work? 

67.  Which  will  dry  more  rapidly,  gloves  washed  with 
water  or  with  gasoline?    Why? 

68.  Why  do  we  cover  utensils  in  cooking? 

69.  How  may  potatoes  be  cooked  in  ten  minutes? 

70.  Explain  why  we  use  a  double  boiler. 

71.  Why  does  water   evaporate    faster   from  a  pan 
than  from  a  bottle? 

72.  Why  is  it  a  waste  of  gas  to  keep  water  boiling 
violently  in  cooking? 

73.  Why  does  a  tea-kettle  have  a  large  bottom? 

74.  Why  does  a  person  feel  chilly  in  damp  clothing? 

75.  Why  does  ethyl  chlorid  freeze  the  tissues? 

76.  Why  do  we  "see  our  breath"  when  it  is  cold? 
Why  not  when  it  is  warm? 

77.  Why  do  one's  glasses  become  covered  with  mist 
on  coming  from  the  cold  into  a  warm  room? 

78.  Why  do  opinions  differ  as  to  whether  a  room  is 
warm  or  cold? 


QUESTIONS  FOR  REVIEW  195 

79.  What  principles  of  physics  are  involved  in  the  use 
of  the  cold  tub  and  the  cold  sponge  in  reducing  temper- 
ature? 

80.  Why  is  the  thunder-clap  not  heard  till  some  time 
after  its  lightning  flash  is  seen? 

81.  Why  are  sounds  heard  better  across  water? 

82.  Why  does  a  person  hear  better  by  placing  the 
hand  behind  the  ear? 

83.  Explain  the  use  of  the  ear- trumpet. 

84.  Why  is  a  grand  piano  used  in  preference  to  an 
upright  for  concerts,  etc.? 

85.  Explain  the  difference  between  men's  and  women's 
voices. 

86.  What  are  some  of  the  conditions  that  may  pro- 
duce deafness? 

87.  Why  does  the  size  of  the  pupil  of  the  eye  change? 

88.  Must  a  person  be  nearer  the  camera  or  farther  away 
for  a  full-length  portrait  than  for  the  head  only? 

89.  Explain  the  intense  heat  produced  by  a  "burning 
glass." 

90.  Why   are   ground-glass   globes   used   on   gas   or 
electric  lights? 

91.  Why  do  the  eyes  become  tired  from  close  work  or 
reading  more  quickly  than  from  looking  at  a  distance? 

92.  Why  do  people  have  two  pairs  of  glasses,  or  those 
with  double  lenses? 

93.  Why    should    very    near-sighted    persons    wear 
glasses  for  reading? 


196  PRACTICAL  PHYSICS  FOR  NURSES 

94.  Why  is  prismatic  glass  used  in  doors  or  windows 
opening  into  dark  corridors? 

95.  Why  should  colors  be  matched  only  in  daylight? 

96.  How  does  an  electric  light  switch  work? 

97.  Why  does  not  an  electric  bell  ring  unless  the 
button  is  pushed? 

98.  What  precautions  must  one  take  in  using  an 
electric  heating  pad? 

99.  Where  would  you  look  for  trouble  if  a  patient's 
bell  failed  to  ring? 

100.  If  an  electric  light  suddenly  went  out,  to  what 
causes  might  it  be  due? 


INDEX 


ACCOMMODATION    in  the   human 

eye,  152 
Adhesion,  24 
Affinity,  chemical,  24 
Air  cells  in  lung,  90 

composition  of,  74 

pressure,  75  et  seq. 
and  boiling,  105 

washing  systems,  96 

weight  of,  75 
Altitude    and   the  boiling-point, 

105,  106 
Ampere,  175 
Apparatus  for  experiments,    17, 

18 

Appliances,  electric,  168  et  seq. 
Arc  light,  170 
Armature,  168 
Artery  clamp,  42 
Artesian  well,  65,  66 
Artificial  aids  to  hearing,  134 

cold,  128 

light,  160 
Atomic  theory,  22 
Atoms,  22,  23 
Attraction,  capillary,  69 
Axis-traction  forceps,  54 

BALL  bearings,  56 

Baths  to  reduce  temperature,  109 

Battery,  electric,  166 

Bell,  electric,  173,  174 

Bismuth  in  x-ray  work,  183 


Block  of  pulley,  50 

Bodily  heat,  production  of,  99 

radiation  of,  126 
Boiling,  104  et  seq. 
Boiling-points,  105 
Bottle,  vacuum,  120 
Bread  mixer,  49 
Breast  pump,  76 
Bulb  syringe,  87 
Buoyancy,  66 
Burning,  100 
Burns  from  x-ray,  184 

CALORIE,  104 
Camera,  156 
Capillarity,  69 

Cathartics,  saline,  action  of,  71 
Cathode  rays,  181 
Cell,  electric,  166 
Center  of  gravity,  33 
Centigrade  thermometer,  104 
Centrifugal  force,  38 
Centrifuge,  38 

Chemical    action    productive    of 
heat,  99 

affinity,  24 

changes,  23,  24 
Chemistry  denned,  21 
Chimney  draft,  92 
Circuit,  electric,  167 
Circulation  in  hot-water  systems, 
122,  124 

of  blood,  88 

197 


i98 


INDEX 


City  water  systems,  65 

Distillation,  110,  111 

Clinical  thermometer,  104 

destructive,  110 

Clothing,  127 

Distilled  water,  111 

Cohesion,  24 

Divers,  deep  sea,  62 

in  liquids,  60 

Draft  in  a  chimney,  92 

Cold  compress,  109 

in  a  stove,  100,  101 

frame,  141 

Drainage  of  wounds,  69 

Color,  158  et  seq. 

Dressing  sterilizer,  107 

waves,  159 

Drops,  size  of,  60 

Compass,  mariner's,  164 

Drowning,  67 

Compressibility  of  gases,  74 

Dry  cells,  electric,  166 

of  liquids,  60 

Ductility,  27 

Condensation  of  liquids,  109 

Dynamo,  167 

Conduction  of  electricity,  175 

of  heat,  115  et  seq. 

EAR,  mechanism  of,  133 

of  sound,  135 

Edema,  71 

Conservation  of  energy,  36 

Elasticity,  27 

Contraction  due  to  cold,  102 

of  gases,  73 

Convection  of  heat,    115,    120  et 

Electric  action  productive  of  heat, 

seq. 

99 

Cooker,  fireless,  119 

appliances,  168  et  seq. 

Cooking  under  pressure,  106 

battery,  166 

Cooling,  artificial,  128 

bell,  173,  174 

by  evaporation,  108,  109 

cell,  166 

Corpuscles,  41 

circuit,  167 

Cracking,  cause  of,  102 

current,  high-frequency,  176 

Crank  and  axle,  49 

flat-iron,  169 

Cream  separator,  37 

fuse,  170 

tester,  68 

heating,  168 

Crookes'  tubes,  180 

lamp,  169 

Crystallization,  28 

lighting,  170 

Crystalloid  substances,  29 

motor,  168 

Cupping  glasses,  76 

switch,  167 

Current,  electric,  166 

telegraph,  172  et  seq. 

high-frequency,  176 

treatments,  176 

wiring,  167,  168 

DEFECTIVE  sight,  153,  154 

Electricity,  163  et  seq. 

Dew,  109 

and  light,  142 

Dialysis,  29 

chemically  produced,  166 

Diffusion,  29,  70 

conductors  of,  175 

of  gases,  73,  91 

faradic,  176 

Dilator,  uterine,  43,  44 

frictional,  164 

INDEX 


199 


Electricity,  galvanic,  176 

how  produced,  164 

produced  by  dynamo,  167 

rate  of  travel,  175 

static,  165,  176 
Electromagnet,  171,  172 
Electron  theory,  23 
Emanation,  radium,  186,  187 
Energy,  35,  36 
Equilibrium,  stable  and  unstable, 

34 

Evaporation,  107  et  seq. 
Expansion  by  heat,  102 
Extension  apparatus,  50 
Eye  defects,  154 

magnet,  172 

the  human,  151,  152 

FAHRENHEIT  thermometer,  104 

Fan  bath,  109 

Faradic  electricity,  176 

Fever,  99 

Field  magnet,  168 

Finsen  light,  159 

Fireless  cooker,  119 

Fireproof  buildings,  sound  in,  137 

Flat-iron,  electric,  169 

Fluoroscope,  183 

Focus  of  light,  151 

of  the  eye,  152  et  seq. 
Force,  centrifugal,  38 

driving,  39 

pump,  86 

the  heart  a,  88 
Forceps,  artery,  42 

obstetric,  54 
Forms  of  matter,  28 
Fountain,  Hero's,  80 

vacuum,  79 
Freezing  of  water,  103 
Friction,  55  et  seq.,  98,  99 
Frictional  electricity,  164 


Frost,  109 
Fulcrum,  41,  45,  47 
Fuse,  electric,  170 

GALVANIC  electricity,  176 

Gas,  illuminating,  74 

Gases  as  conductors  of  heat,  117 

diffusion  of,  73,  91 

properties  of,  73 

structure  of,  28 
Gravity,  32 

center  of,  33 

specific,  33,  60 

HARDNESS,  27 
Head  mirror,  154 
Hearing,  aids  to,  134 

mechanism  of,  133 
Heart,  action  of,  88 

sounds,  138 
Heat,  98 

bodily,  99,  126 

effects  of,  102 

latent,  127 

measurement  of,  103 

retention  of,  119 

sources  of,  98 

transmission  of,  115  et  seq. 
Heating,  electric,  168 

systems,  121  et  seq. 
High-frequency  electric  current, 

176 

Hoarseness,  137 
Hot-water  heating,  124 
Human  voice,  132 
Hydraulics,  60 

denned,  30 
Hydrometer,  67 
Hypodermic  syringe,  81 

ICE-CREAM  freezer,  49,  128 
Illuminated  objects,  146 


INDEX 


Illuminating  gas,  74 
Impenetrability,  35 
Importance  of  physics,  19 
Incandescent  electric  lights,  170 
Inclined  plane,  51 
Induction  coil,  176 
Inertia,  26 

Instruments,  optical,  154  et  seq. 
Insulators,  electric,  175 
Interference  with  sound,  137 
Irrigators,  62,  63 

JOINTS,  construction  of  human, 
56,  57 

KITCHEN  range,  drafts  in,   100, 

101 
for  heating  water,  122 

LAMP,  electric,  169 
Laryngoscope,  156 
Latent  heat,  127,  128 
Law,  Newton's,  37 

of  Archimedes,  66 

Pascal's,  64 
Laws  of  air  pressure,  80  et  seq. 

of  motion,  37 
Lead  in  x-ray  work,  184 
Lens  of  the  eye,  151  . 
Lenses,  149,  150 
Lever,  41  et  seq. 

Stanhope,  29 

Levers  in  the  human  body,  44,  47, 
48 

of  the  first  class,  41-44 

of  the  second  class,  45,  46 

of  the  third  class,  47 
Leyden  jar,  165 
Lifting  pump,  85 
Light,  141  et  seq. 

arc,  170 

artificial,  160 


Light,  direction  of,  142 

electric,  170 

incandescent,  169,  170 

intensity  of,  142,  143 

rays  of,  142 

reflection  of,  146,  157 

refraction  of,  148 

transmission  of,  141,  144 

waves,  141 
Liquids,  compressibility  of,  60 

pressure  in,  61  et  seq. 

properties  of,  60 

structure  of,  28 

weight  of,  61 
Lubricants,  56 
Luminous  objects,  145 
Lung  sounds,  138 
Lungs,  action  of,  90 

MACHINE,  the  human,  39 
Machines,  38  et  seq. 

classes  of,  41 
Magnetism,  163 
Magnets,  163 

electro-,  171,  172 

eye,  172 

field,  168 
Malleability,  27 
Matching  colors,  160, 
Matter,  composition  of,  21 

forms  of,  28 

properties  of,  24 
Measurement  of  heat,  103,  104 
Measures,  electric,  175 
Mechanics,  32  et  seq. 

defined,  30 

of  obstetrics,  52 
Medical  uses  of  electricity,  176 
of  radium,  187 
of  the  x-ray,  184 
Microscope,  157 

adjustment  of,  51 


INDEX 


201 


Mirror,  reflection  in,  142,  143 
Molecular  motion,  98 
Molecules,  22,  24 
Motion,  25 

laws  of,  37,  38 
Motors,  electric,  168 
Muscles  as  levers,  44,  47,  48 

as  pulleys,  51 
Music,  136,  138 

NOISE  vs.  music,  138 
Normal  temperature,  99 

OBSTETRIC  forceps,  54 

Obstetrics,  mechanics  of,  52,  64 

Ohm,  175 

Opacity,  27 

Ophthalmoscope,  155 

Optical  instruments,  153  et  seq. 

Osmosis,  70,  71 

Oxygen  in  combustion.  100 

PARTICLE,  22 
Pascal's  law,  64 
Penumbra,  144 

Perspiration,  action  of,  108,  109 
Phonendoscope,  136 
Photographs  by  jc-ray,  181 
Physical  changes,  23,  24 
Physics  denned,  21 

importance  of,  19 
Pitch  of  sounds,  136 
Plane,  inclined,  51 
Plenum  system  of  ventilation,  95 
Pliers,  42 

Plumbing  in  kitchen,  ±21 
Pneumatics,  30,  73  et  seq. 
Polarization  of  light,  151 
Porosity,  26 
Power  in  levers,  41  et  seq. 

in  machinery,  39 
Pressure  in  liquids,  64 


Pressure  in  steam  apparatus,  106 
et  seq. 

of  air,  75  et  seq. 
Primary  colors,  158 
Prism,  158 
Properties  of  gases,  73 

of  liquids,  60 

of  matter,  24,  25,  27 
Pulley,  50 
Pumps,  85,  86 

QUESTIONS  for  review,  190 

RADIANT  matter,  185 
Radiation  of  heat,  125  et  seq. 
Radium,  185 

compounds  of,  186 

emanation,  186,  187 

history  of,  185 

uses  of,  187 

Rain,  production  of,  109 
Rate  of  travel  of  electricity,  175 
of  light,  141 
of  sound,  135 
Rays,  radium,  187 

x-,  180 
Reaction,  38 
Reflection  of  light,  146,  147 

of  sound,  137 
Refraction  of  light,  148 
Refrigerators,  117,  118 
Respiration,  90,  91 
Review  questions,  190 
Roentgen  rays,  180  et  seq. 
Rolling  friction,  56 

SALINE  cathartics,  71 
Scissors,  42,  44 
Screwdriver,  51 
Separator  for  cream,  37 
Sewing  machine,  49 
Shadows,  formation  of,  144 


202 


INDEX 


Sheave,  50 

Sight,  145,  151  et  seq. 

Siphon,  81,  82 

Sliding  friction,  55 

Snow,  how  produced,  109 

Solids,  structure,  28 

Sound,  130  et  seq. 

conduction  of,  135 

interference  with,  137 

reflection  of,  137 

speed  of,  135 

Sounds  of  heart  and  lungs,  138 
Specific  gravity,  33,  60,  68 
Speculum,  bivalve,  43 
Sphygmomanometer,  89 
Stability,  34 
Standing,  34,  35 
Stanhope  lever,  49 
Static  electricity,  165 
Steam  apparatus,  89 

engine,  89 

heating  system,  124 

pressure  apparatus,  106  et  seq. 
Sterilizers,  107 
Stethoscope,  135 
Stomach-tube,  83 
Subnormal  temperature,  100 
Substances,  simple  and  complex, 

21 

Sunstroke,  127 
Supplies  for  experiments,  17 
Swimming,  67 
Switch,  electric,  167 
Synovial  fluid,  57 
Syringe,  bulb,  87 

hypodermic,  81 
Systems  of  heating,  121  et  seq. 

of  ventilation,  94 

TELEGRAPH,  172  et  seq. 
Telephone,  173 
Telescope,  158 


Temperature,  bodily,  99,  100 

defined,  101 

its  relation  to  form,  28 
Tenacity,  27 

Tendency  to  crystallize,  28 
Testing  milk,  68 

Theories  in  regard  to  radium,  185 
Theory,  atomic,  22 

electron,  23 

Thermometers,  103,  104 
Transmission  of  light,  144 
Transparency,  27 
Treatments,  electric,  176 

with  radium,  187 

URINALYSIS,    polarized   light   in, 

151 
Urine  centrifuge,  38 

pressure  in  bladder,  64 
Urinometer,  68 
Uterine  dilators,  44,  52 

VACUUM,  77 

bottle,  120 

fountain,  79 

kettle,  106 

system  of  ventilation,  95 

tube,  180 

Valves  in  veins,  89 
Venous  circulation,  89 
Ventilating  systems,  94 
Ventilation,  91  et  seq. 
Vibrations  producing  sound,  130, 

136 

Vibreur,  electric,  172 
Voice,  human,  132,  136 
Volt,  175 

WALKING,  34,  35 
Washed  air  ventilating  system,  96 
Water  as  a  conductor  of  heat,  1 16 
bed,  64 


INDEX 


203 


Water,  distilled,  111 

freezing  of,  103 

heating  system,  122,  124 

sterilizers,  107 

systems,  65 
Waterproofing,  70 
Watt,  175 

Wave  movement  of  sounds,  131 
Waves  in  colored  light,  159 

of  light,  141 
Wedge,  52 
Weight,  33 

of  air,  75 


Weight  of  liquids,  61 

Weights  moved  with  lever,  41  et 

seq. 

Well,  artesian,  65 
Wheel  and  axle,  49 
Wiring,  electric,  167,  168 
Work,  35,  36 
Wounds,  drainage  of,  69 

JJC-RAY,  180  et  seq. 
burns  from,  184 
characteristics  of,  181 
uses  of,  183 


bOO"94l"356 8 


LIBRARY 

ANGELES,  CAUF, 


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